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High-End Performance with Low-End Hardware: Analysis of Massive MIMO Base Station Transceivers
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-2093-5466
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Massive MIMO (multiple-input–multiple-output) is a multi-antenna technology for cellular wireless communication, where the base station uses a large number of individually controllable antennas to multiplex users spatially.  This technology can provide a high spectral efficiency.  One of its main challenges is the immense hardware complexity and cost of all the radio chains in the base station.  To make massive MIMO commercially viable, inexpensive, low-complexity hardware with low linearity has to be used, which inherently leads to more signal distortion.  This thesis investigates how the degenerated linearity of some of the main components—power amplifiers, analog-to-digital converters (ADCs) and low-noise amplifiers—affects the performance of the system, with respect to data rate, power consumption and out-of-band radiation. The main results are: Spatial processing can reduce PAR (peak-to-average ratio) of the transmit signals in the downlink to as low as 0B; this, however, does not necessarily reduce power consumption.  In environments with isotropic fading, one-bit ADCs lead to a reduction in effective signal-to-interference-and-noise ratio (SINR) of 4dB in the uplink and four-bit ADCs give a performance close to that of an unquantized system.  An analytical expression for the radiation pattern of the distortion from nonlinear power amplifiers is derived.  It shows how the distortion is beamformed to some extent, that its gain never is greater than that of the desired signal, and that the gain of the distortion is reduced with a higher number of served users and a higher number of channel taps.  Nonlinear low-noise amplifiers give rise to distortion that partly combines coherently and limits the possible SINR.  It is concluded that spatial processing with a large number of antennas reduces the impact of hardware distortion in most cases.  As long as proper attention is paid to the few sources of coherent distortion, the hardware complexity can be reduced in massive MIMO base stations to overcome the hardware challenge and make massive MIMO commercial reality.

Abstract [sv]

Massiv MIMO (eng: multiple-input–multiple-output) är en flerantennsteknologi för cellulär trådlös kommunikation, där basstationen använder ett stort antal individuellt styrbara antenner för att multiplexa användare i rummet.  Denna teknologi kan tillhandahålla en hög spektral effektivitet.  En av dess främsta utmaningar är den enorma hårdvarukomplexiteten och kostnaden hos basstationens alla radiokedjor.  För att massiv MIMO skall bli kommersiellt attraktivt, måste billiga, enkla hårdvarukomponenter med låg linjäritet användas, vilket oundvikligen leder till mer signaldistorsion.  Denna avhandling undersöker hur den försämrade linjäriteten hos några av huvudkomponenterna – effektförstärkare, analog-digital-omvandlare (AD-omvandlare) och lågbrusförstärkare – påverkar systemets prestanda, i termer av datatakt, effektförbrukning och utombandsstrålning.  Huvudresultaten är: Rumslig signalbehandling kan reducera sändsignalernas toppvärde i nerlänken ända ner till 0dB, vilket dock inte nödvändigtvis minskar effektförbrukningen.  I miljöer med isotrop fädning leder enbits-AD-omvandlare till 4dB lägre signal-till-interferens-och-brus-förhållande i upplänken, och fyrabits-AD-omvandlare ger en prestanda nära den ett system utan kvantisering kan uppnå.  Ett analytiskt uttryck för strålningsmönstret för distorsionen från icke-linjära effektförstärkare härleds.  Det visar hur distorsionen till viss del lobformas, att dess förstärkning aldrig är starkare än förstärkningen för den önskade signalen och att distorsionens förstärkning minskar med ett högre antal betjänade användare och ett högre antal kanaltappar.  Icke-linjära lågbrusförstärkare ger upphov distorsion som delvis kombinerar koherent och begränsar det möjliga signal-till-brus-och-interferens-förhållandet.  Slutsatsen är att rumslig signalbehandling med ett stort antal antenner reducerar hårdvarudistorsionens inverkan i de flesta fall.  Så länge som de få källorna till koherent distorsion ges tillbörlig uppmärksamhet, kan hårdvarukomplexiteten minskas i basstationer för massiv MIMO för att övervinna hårdvaruutmaningen och göra massiv MIMO kommersiell verklighet.

Abstract [zh]

蜂窩無線通訊領域中的大規模多天線技術以多個單獨可控的天線通過空間複用的方式服務多個用戶。如是可以大幅提高頻譜效率。實現此技術的主要難題在於基站所用射頻單元的極大複雜度及成本。爲使大規模多天線技術適用在商業系統中,需使用導致失真的低複雜度低成本的非線性硬件。本文探討若將一些主要部件——功放、模數轉換器、低噪聲放大器——的線性程度降低,系統性能是如何受到影響的,即系統的速率、功耗、帶外泄露等指標。主要的結果爲:空間信號處理可以降低下行信號的峯均比,直至0分貝;然而低峯均比不一定能夠降低功耗。用一比特模數轉換器使上行的信干噪比減少4分貝;用四比特模數轉換器可在各向同性衰落的環境裏實現接近無量化系統的性能。本文推導出非線性功放失真輻射方向的解析公式。該公式展示失真在某種程度上會被波束成形的;具體而言,失真的波束成形增益不大於有效信號的增益,波束成形增益會根據服務用戶數量和信道階數的增長而降低。非線性低噪聲放大器引起的失真,一部分會相干地合併,因此會限制信干噪比的增長。結論爲多天線的空間信號處理可以減少硬件失真的影響。只要適當地處理少數相干失真的來源,大規模多天線基站可以降低硬件複雜度,解決硬件難題,使大規模多天線技術成功地應用在商業系統中成爲現實。

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , p. 90
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1896
Keyword [sv]
Beamforming, distortion, massive MIMO, MIMO, nonlinear hardware, peak-to-average ratio
National Category
Signal Processing Telecommunications Communication Systems Other Electrical Engineering, Electronic Engineering, Information Engineering Computer Engineering
Identifiers
URN: urn:nbn:se:liu:diva-143455DOI: 10.3384/diss-diva-143455ISBN: 9789176853887 (print)OAI: oai:DiVA.org:liu-143455DiVA, id: diva2:1163832
Public defence
2018-01-26, Ada Lovelace, B-huset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2018-01-03 Created: 2017-12-08 Last updated: 2018-03-14Bibliographically approved
List of papers
1. Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance
Open this publication in new window or tab >>Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance
2016 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 46, no 12, p. 5050-5063Article in journal (Refereed) Published
Abstract [en]

In massive multiple-input multiple-output (MIMO), most precoders result in downlink signals that suffer from high peak-to-average ratio (PAR), independently of modulation order and whether single-carrier or orthogonal frequency-division multiplexing (OFDM) transmission is used. The high PAR lowers the power efficiency of the base-station amplifiers. To increase the power efficiency, low-PAR precoders have been proposed. In this paper, we compare different transmission methods for massive MIMO in terms of the power consumed by the amplifiers. It is found that: 1) OFDM and single-carrier transmission have the same performance over a hardened massive MIMO channel and 2) when the higher amplifier power efficiency of low-PAR precoding is taken into account, conventional and low-PAR precoders lead to approximately the same power consumption. Since downlink signals with low PAR allow for simpler and cheaper hardware, than signals with high PAR, therefore, the results suggest that low-PAR precoding with either single-carrier or OFDM transmission should be used in a massive MIMO base station.

Place, publisher, year, edition, pages
IEEE, 2016
National Category
Communication Systems
Identifiers
urn:nbn:se:liu:diva-130514 (URN)10.1109/TCOMM.2016.2557781 (DOI)000391694500013 ()
Funder
EU, FP7, Seventh Framework Programme, ICT-619086Swedish Research CouncilELLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
Note

Funding agencies: European Union [ICT-619086]; Swedish Research Council (Vetenskapsradet); ELLIIT

Available from: 2016-08-11 Created: 2016-08-11 Last updated: 2018-01-03
2. Multiuser MIMO Precoding with Per-Antenna Continuous-Time Constant-Envelope Constraints
Open this publication in new window or tab >>Multiuser MIMO Precoding with Per-Antenna Continuous-Time Constant-Envelope Constraints
2015 (English)In: 2015 IEEE 16th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 261-265Conference paper, Published paper (Refereed)
Abstract [en]

A transmission scheme for the multiuser MIMO downlink, where the transmit signal from each antenna has constant envelope and a limited bandwidth, is proposed in order to enable the use of highly efficient, nonlinear amplifiers at the base station. To evaluate its performance, an achievable rate is derived and the necessary transmit power of the proposed scheme is computed for a system with 40 antennas that serves 4 users at data rates around 1 bpcu. For this system and 40% excess 30 dB-bandwidth, approximately 3 dB more transmit power is required to achieve the same sum-rate as without the constantenvelope constraints.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2015
Series
IEEE International Workshop on Signal Processing Advances in Wireless Communications, ISSN 2325-3789
National Category
Communication Systems
Identifiers
urn:nbn:se:liu:diva-120251 (URN)10.1109/SPAWC.2015.7227040 (DOI)000380547100053 ()978-1-4799-1931-4 (ISBN)
Conference
SPAWC 2015 The 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, June 28 – July 1, 2015, Stockholm, Sweden
Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2018-01-03Bibliographically approved
3. Uplink Performance of Wideband Massive MIMO With One-Bit ADCs
Open this publication in new window or tab >>Uplink Performance of Wideband Massive MIMO With One-Bit ADCs
2017 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 1, p. 87-100Article in journal (Refereed) Published
Abstract [en]

Analog-to-digital converters (ADCs) stand for a significant part of the total power consumption in a massive multiple-input multiple-output (MIMO) base station. One-bit ADCs are one way to reduce power consumption. This paper presents an analysis of the spectral efficiency of single-carrier and orthogonal-frequency-division-multiplexing (OFDM) transmission in massive MIMO systems that use one-bit ADCs. A closed-form achievable rate, i.e., a lower bound on capacity, is derived for a wideband system with a large number of channel taps that employ low-complexity linear channel estimation and symbol detection. Quantization results in two types of error in the symbol detection. The circularly symmetric error becomes Gaussian in massive MIMO and vanishes as the number of antennas grows. The amplitude distortion, which severely degrades the performance of OFDM, is caused by variations between symbol durations in received interference energy. As the number of channel taps grows, the amplitude distortion vanishes and OFDM has the same performance as single-carrier transmission. A main conclusion of this paper is that wideband massive MIMO systems work well with one-bit ADCs.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2017
Keyword
MIMO, Channel estimation, Wideband, Quantization (signal), Distortion, Fading channels, One-bit ADCs
National Category
Communication Systems
Identifiers
urn:nbn:se:liu:diva-135783 (URN)10.1109/TWC.2016.2619343 (DOI)000393876200007 ()2-s2.0-85009814512 (Scopus ID)
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2018-01-03Bibliographically approved
4. Achievable Uplink Rates for Massive MIMO with Coarse Quantization
Open this publication in new window or tab >>Achievable Uplink Rates for Massive MIMO with Coarse Quantization
2017 (English)In: 2017 IEEE InternationalConference on Acoustics, Speech,and Signal Processing Proceedings, 2017, p. 6488-6492Conference paper, Published paper (Refereed)
Abstract [en]

The high hardware complexity of a massive MIMO base station, which requires hundreds of radio chains, makes it challenging to build commercially.  One way to reduce the hardware complexity and power consumption of the receiver is to lower the resolution of the analog-to-digital converters (ADCs).  We derive an achievable rate for a massive MIMO system with arbitrary quantization and use this rate to show that ADCs with as low as 3 bits can be used without significant performance loss at spectral efficiencies around 3.5 bpcu per user, also under interference from stronger transmitters and with some imperfections in the automatic gain control.

Series
Acoustics, Speech and Signal Processing (ICASSP), E-ISSN 2379-190X ; 2017
Keyword
ADC, channel estimation, low resolution, massive MIMO, quantization
National Category
Communication Systems
Identifiers
urn:nbn:se:liu:diva-135787 (URN)10.1109/ICASSP.2017.7953406 (DOI)000414286206131 ()9781509041176 (ISBN)9781509041169 (ISBN)9781509041183 (ISBN)
Conference
International Conference on Acoustics, Speech, and Signal Processing, March 5–9, 2017, New Orleans, USA
Note

Funding agencies: European Union Seventh Framework Programme [ICT-619086]; Swedish Research Council (Vetenskapsradet); National Science Foundation [NSF-CCF-1527079]; ICT R&D program of MSIP/IITP [2016 (B0717-16-0002)]

Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2018-01-12Bibliographically approved

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