liu.seSearch for publications in DiVA
Change search
Refine search result
1 - 20 of 20
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Kashyap, Salil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Frequency-Domain Interpolation of the Zero-Forcing Matrix in Massive MIMO-OFDM2016In: 2016 IEEE 17TH INTERNATIONAL WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS (SPAWC), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    We consider massive multiple input multiple output (MIMO) systems with orthogonal frequency division multiplexing (OFDM) that use zero-forcing (ZF) to combat interference. To perform ZF, large dimensional pseudo-inverses have to be computed. In this paper, we propose a discrete Fourier transform (DFT)-interpolation-based technique where substantially fewer ZF matrix computations have to be done with very little deterioration in data rate compared to computing an exact ZF matrix for every subcarrier. We claim that it is enough to compute the ZF matrix at L(amp;lt;amp;lt; N) selected subcarriers where L is the number of resolvable multipaths and N is the total number of subcarriers and then interpolate. The proposed technique exploits the fact that in the massive MIMO regime, the ZF impulse response consists of L dominant components. We benchmark the proposed method against full inversion, piecewise constant and linear interpolation methods and show that the proposed method achieves a good tradeoff between performance and complexity.

  • 2.
    Kashyap, Salil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Emil, Björnson
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Performance Analysis of (TDD) Massive MIMO with Kalman Channel Prediction2017In: Acoustics, Speech and Signal Processing (ICASSP), 2017 IEEE International Conference on, 2017, p. 3554-3558Conference paper (Refereed)
    Abstract [en]

    In massive MIMO systems, which rely on uplink pilots to estimate the channel, the time interval between pilot transmissions constrains the length of the downlink.  Since switching between up- and downlink takes time, longer downlink blocks increase the effective spectral efficiency.  We investigate the use of low-complexity channel models and Kalman filters for channel prediction, to allow for longer intervals between the pilots.  Specifically, we quantify how often uplink pilots have to be sent when the downlink rate is allowed to degrade by a certain percentage.  To this end, we consider a time-correlated channel aging model, whose spectrum is rectangular, and use autoregressive moving average (ARMA) processes to approximate the time-variations of such channels.  We show that ARMA-based predictors can increase the interval between pilots and the spectral efficiency in channels with high Doppler spreads.  We also show that Kalman prediction is robust to mismatches in the channel statistics.

  • 3.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Achievable Rate Analysis for Massive MIMO Base Stations with One-Bit ADCs2016Data set
  • 4.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    High-End Performance with Low-End Hardware: Analysis of Massive MIMO Base Station Transceivers2017Doctoral 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.

    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
    Keywords
    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
    Keywords
    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
    5. Out-of-Band Radiation from Large Antenna Arrays
    Open this publication in new window or tab >>Out-of-Band Radiation from Large Antenna Arrays
    Show others...
    2018 (English)In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 56, no 4, p. 196-203Article in journal (Refereed) Published
    Abstract [en]

    The OOB radiation from large arrays with nonlinear hardware has a different radiation pattern than the beamformed in-band signal. This is the main difference between the OOB radiation from large arrays and from well-studied legacy systems. Beamforming might focus the OOB radiation in certain directions but also significantly reduce the total power that has to be transmitted. For cost and power-consumption reasons, large arrays might have to be built from low-complexity hardware without advanced pre-compensation for linearization, which increases the relative amount of OOB radiation. Given that large arrays will be used in future base stations, a correct understanding of the OOB radiation is crucial to specify appropriate linearity requirements for the hardware. We show that the OOB radiation from large arrays varies little between coherence times; it is isotropic in many cases; and when it is beamformed, it is directed toward the served user in a very narrow beam with an array gain equal to or less than that of the in-band signal. We draw the conclusion that, compared to legacy systems, less stringent linearity requirements can be used in many systems with large arrays by virtue of the lower transmit power needed to upkeep the same received signal-to-noise ratio.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
    National Category
    Signal Processing
    Identifiers
    urn:nbn:se:liu:diva-147809 (URN)10.1109/MCOM2018.1601063 (DOI)000430412200028 ()
    Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-11-29
    6. Spatial Characteristics of Distortion Radiated From Antenna Arrays With Transceiver Nonlinearities
    Open this publication in new window or tab >>Spatial Characteristics of Distortion Radiated From Antenna Arrays With Transceiver Nonlinearities
    2018 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 10, p. 6663-6679Article in journal (Refereed) Published
    Abstract [en]

    The distortion from massive multiple-input multiple-output base stations with nonlinear amplifiers is studied and its radiation pattern is derived. The distortion is analyzed both in-band and out-of-band. By using an orthogonal Hermite representation of the amplified signal, the spatial cross-correlation matrix of the nonlinear distortion is obtained. It shows that, if the input signal to the amplifiers has a dominant beam, the distortion is beamformed in the same way as that beam. When there are multiple beams without any one being dominant, it is shown that the distortion is practically isotropic. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the out-of-band radiation, to do reciprocity calibration, and to schedule users in the frequency plane to minimize the effect of in-band distortion.

    Place, publisher, year, edition, pages
    IEEE, 2018
    Keywords
    Amplifiers; distortion; in-band distortion; massive multiple-input multiple-output; nonlinear; out-of-band radiation; reciprocity calibration; spectral regrowth
    National Category
    Signal Processing
    Identifiers
    urn:nbn:se:liu:diva-152397 (URN)10.1109/TWC.2018.2861872 (DOI)000447047200021 ()
    Note

    Funding Agencies|Swedish Research Council (VR); ELLIIT; VINNOVA

    Available from: 2018-10-30 Created: 2018-10-30 Last updated: 2018-11-29
    7. Impact of Spatial Filtering on Distortion From Low-Noise Amplifiers in Massive MIMO Base Stations
    Open this publication in new window or tab >>Impact of Spatial Filtering on Distortion From Low-Noise Amplifiers in Massive MIMO Base Stations
    2018 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 12, p. 6050-6067Article in journal (Refereed) Published
    Abstract [en]

    In massive multiple-input-multiple-output base stations, power consumption and cost of the low-noise amplifiers (LNAs) can be substantial because of the many antennas. We investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. A polynomial model is used to characterize the nonlinear LNAs and to derive the second-order statistics and spatial correlation of the distortion. We show that, with spatial matched filtering (maximum-ratio combining) at the receiver, some distortion terms combine coherently, and that the signal-to-interference-and-noise ratio of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, it is studied how the power from a blocker in the adjacent frequency band leaks into the main band and creates distortion. The distortion term that scales cubically with the power received from the blocker has a spatial correlation that can be filtered out by spatial processing and only the coherent term that scales quadratically with the power remains. When the blocker is in free-space line-of-sight and the LNAs are identical, this quadratic term has the same spatial direction as the desired signal, and hence cannot be removed by linear receiver processing.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
    Keywords
    Amplifiers; antenna arrays; multiple-input-multiple-output (MIMO) systems; nonlinear distortion; nonlinearities
    National Category
    Signal Processing
    Identifiers
    urn:nbn:se:liu:diva-153681 (URN)10.1109/TCOMM.2018.2850331 (DOI)000454112200017 ()
    Conference
    51st IEEE Asilomar Conference on Signals, Systems, and Computers
    Note

    Funding Agencies|VINNOVA; Vetenskapsradet (Swedish Research Council); ELLIIT; Chalmers; Ericsson; RUAG; SAAB

    Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-01-14
  • 5.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Low-PAR Precoding for Very-Large Multi-User MIMO Systems2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Very-large multi-user MIMO systems, with hundreds of base station antennae, are increasingly attracting attention from both academia and industry. One reason is that such systems can use multi-user precoding to simultaneously serve multiple single-antenna users over the same time-frequency resource. This implies increased data rates and improved spectral efficiency. Another reason is that the energy consumed by the base station is expected to decrease linearly with the number of antennae because of the increasing array gain. To enable the massive increase in the number of antennae, each antenna, together with its tranceiver chain, has to be cheap. If one could manufacture base station antennae using low-cost, mass-produced handset technology, including power amplifiers without advanced linearisation techniques, then very-large multi-user MIMO could become reality.

    Handset power amplifiers generally aim to be power-efficient, and in doing so often have highly non-linear transfer characteristics. It is of benefit to transmit signals with low peak-to-average ratio (PAR) through such power amplifiers, to avoid excessive distortion and to maximise the power efficiency by only having small operating back-offs. Conventionally precoded signals unfortunately have high PAR (approx. 10 dB). This work has investigated the low-PAR precoding scheme for very-large MIMO proposed by Mohammed et al. (2013a). It is shown that, the transmit signals of this precoding scheme have 4 dB PAR, and that by further limiting the phase variation, the PAR can be made arbitrarily small. However, the more the phase is constrained, the smaller the array gain will be. For example, if the phase variation is limited to π/2, the PAR is lowered to 2.6 dB, but 2-3 dB more transmit power is needed to maintain the same performance or, equivalently, 1.6-2.0 times more antennae are needed at the base station. Continuous phase modulation has briefly been studied as a means of producing constant-envelope transmit signals. Low-PAR precoding, where the transmit signals lie inside a circle, is suggested as a way to decrease the required transmit power without increasing PAR noticeably (<4.5 dB) relative to scheme of Mohammed et al. The algorithm that was developed for this purpose, however got stuck in local minima, which degraded its performance. The transmit power could therefore only be slightly (<1 dB) lowered in the regime of high data rates.

    A preliminary link budget analysis based on a simplistic model of the power amplifier has shown that, assuming perfect channel state information and frequency-flat fading, low-PAR precoding can reduce energy consumption by 33 % compared to conventional linear precoding in a base station with 100 antennae. The analysis suggests that using unlinearised class AB handset power amplifiers might be a viable option for very-large multi-user MIMO base stations.

  • 6.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    On Massive MIMO Base Stations with Low-End Hardware2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Massive MIMO (Multiple-Input Multiple-Output) base stations have proven, both in theory and in practice, to possess many of the qualities that future wireless communication systems will require.  They can provide equally high data rates throughout their coverage area and can concurrently serve multiple low-end handsets without requiring wider spectrum, denser base station deployment or significantly more power than current base stations.  The main challenge of massive MIMO is the immense hardware complexity and cost of the base station—each element in the large antenna array needs to be individually controllable and therefore requires its own radio chain.  To make massive MIMO commercially viable, the base station has to be built from inexpensive simple hardware.  In this thesis, it is investigated how the use of low-end power amplifiers and analog-to-digital converters (ADCs) affects the performance of massive MIMO.  In the study of the signal distortion from low-end amplifiers, it is shown that in-band distortion is negligible in massive MIMO and that out-of-band radiation is the limiting factor that decides what power efficiency the amplifiers can be operated at.  A precoder that produces transmit signals for the downlink with constant envelope in continuous time is presented to allow for highly power efficient low-end amplifiers.  Further, it is found that the out-of-band radiation is isotropic when the channel is frequency selective and when multiple users are served; and that it can be beamformed when the channel is frequency flat and when few users are served.  Since a massive MIMO base station radiates less power than today's base stations, isotropic out-of-band radiation means that low-end hardware with poorer linearity than required today can be used in massive MIMO.  It is also shown that using one-bit ADCs—the simplest and least power-hungry ADCs—at the base station only degrades the signal-to-interference-and-noise ratio of the system by approximately 4 dB when proper power allocation among users is done, which indicates that massive MIMO is resistant against coarse quantization and that low-end ADCs can be used.

    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. Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission
    Open this publication in new window or tab >>Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission
    2016 (English)In: 2016 IEEE International Conference on Communications (ICC), IEEE , 2016, p. 1-6Conference paper, Published paper (Refereed)
    Abstract [en]

    The spatial characteristics of the out-of-band radiation that a multiuser MIMO system emits, due to its power amplifiers (modeled by a polynomial model) being nonlinear, are studied by deriving an analytical expression for the continuous-time cross-correlation of the transmit signals.  It is shown that, at any spatial point and on any frequency, the received power averaged over many channel realizations from a MIMO base station is the same as from a SISO base station when the two radiate the same amount of power.  For a specific channel realization however, the received power can deviate from this average.  We show that the deviations from the average are small in a MIMO system with multiple users and that the deviations can be significant with only one user.  Using an ergodicity argument, we conclude that out-of-band radiation is less of a problem in massive MIMO, where precoding and array gain let us reduce the total radiated power compared to SISO systems.  The requirements on spectral regrowth can therefore be relaxed in MIMO systems without causing more total out-of-band radiation.

    Place, publisher, year, edition, pages
    IEEE, 2016
    Series
    IEEE International Conference on Communications, ISSN 1550-3607
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-130513 (URN)10.1109/ICC.2016.7511629 (DOI)000390993205153 ()9781479966646 (ISBN)
    Conference
    2016 IEEE International Conference on Communications (ICC), 22-27 May 2016, Kuala Lumpur, Malaysia
    Funder
    EU, FP7, Seventh Framework Programme, ICT-619086Swedish Research Council
    Available from: 2016-08-11 Created: 2016-08-11 Last updated: 2017-01-29Bibliographically approved
    4. 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
    Keywords
    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
  • 7.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Choi, Junil
    POSTECH, South Korea.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Heath, Robert W.
    University of Texas at Austin, USA.
    Achievable Uplink Rates for Massive MIMO with Coarse Quantization2017In: 2017 IEEE InternationalConference on Acoustics, Speech,and Signal Processing Proceedings, 2017, p. 6488-6492Conference 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.

  • 8.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Choi, Junil
    University of Texas at Austin,USA.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Heath, Robert W.
    University of Texas at Austin,USA.
    One-Bit ADCs in Wideband Massive MIMO Systems with OFDM Transmission2016In: 2016 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING PROCEEDINGS, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 3386-3390Conference paper (Refereed)
    Abstract [en]

    We investigate the performance of wideband massive MIMO base stations that use one-bit ADCs for quantizing the uplink signal. Ourmain result is to show that the many taps of the frequency-selective channel make linear combiners asymptotically consistent and the quantization noise additive and Gaussian, which simplifies signal processing and enables the straightforward use of OFDM . We also find that single-carrier systems and OFDM systems are affected in the same way by one-bit quantizers in wideband systems because the distribution of the quantization noise becomes the same in both systems as the number of channel taps grows.

  • 9.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Choi, Junil
    Department of Electrical Engineering, Pohang University of Science and Technology, Pohang, South Korea.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Heath, Robert W.
    Wireless Networking and Communications Group, The University of Texas at Austin, Austin, TX, USA.
    Uplink Performance of Wideband Massive MIMO With One-Bit ADCs2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 1, p. 87-100Article in journal (Refereed)
    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.

  • 10.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustavsson, Ulf
    Ericsson Research, Gothenburg, Sweden.
    Eriksson, Thomas
    Chalmers University of Technology, Gothenburg, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Analysis of nonlinear low-noise amplifiers in massive MIMO base stations2017In: 2017 51st Asilomar Conference on Signals, Systems, and Computers, 2017, p. 285-289Conference paper (Refereed)
    Abstract [en]

    Because of the large number of antennas at the base station, the power consumption and cost of the low-noise amplifiers (LNAs) can be substantial. Therefore, we investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. To characterize the nonlinear distortion, we describe the LNAs using a polynomial model, which allows for the derivation of the second-order statistics of the received signal and the distortion. A massive MIMO system that serves one user in line-of-sight is studied. It is shown that the distortion from the LNAs combines coherently and that the SINR of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, the impact of a strong transmitter in the adjacent frequency band is investigated. The second-order statistics show how the power from that transmission leaks into the main band and interferes with the symbol estimates.

  • 11.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Ericsson, Sweden; Ericsson, Peoples R China; Eidgenoss TH Zurich, Switzerland; Univ Texas Austin, TX 78712 USA; Apple, CA 92307 USA.
    Gustavsson, Ulf
    Ericsson Res, Sweden.
    Eriksson, Thomas
    Chalmers Univ Technol, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Impact of Spatial Filtering on Distortion From Low-Noise Amplifiers in Massive MIMO Base Stations2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 12, p. 6050-6067Article in journal (Refereed)
    Abstract [en]

    In massive multiple-input-multiple-output base stations, power consumption and cost of the low-noise amplifiers (LNAs) can be substantial because of the many antennas. We investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. A polynomial model is used to characterize the nonlinear LNAs and to derive the second-order statistics and spatial correlation of the distortion. We show that, with spatial matched filtering (maximum-ratio combining) at the receiver, some distortion terms combine coherently, and that the signal-to-interference-and-noise ratio of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, it is studied how the power from a blocker in the adjacent frequency band leaks into the main band and creates distortion. The distortion term that scales cubically with the power received from the blocker has a spatial correlation that can be filtered out by spatial processing and only the coherent term that scales quadratically with the power remains. When the blocker is in free-space line-of-sight and the LNAs are identical, this quadratic term has the same spatial direction as the desired signal, and hence cannot be removed by linear receiver processing.

  • 12.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustavsson, Ulf
    Ericsson Research, Sweden.
    Eriksson, Thomas
    Chalmers tekniska högskola, Göteborg, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission2016In: 2016 IEEE International Conference on Communications (ICC), IEEE , 2016, p. 1-6Conference paper (Refereed)
    Abstract [en]

    The spatial characteristics of the out-of-band radiation that a multiuser MIMO system emits, due to its power amplifiers (modeled by a polynomial model) being nonlinear, are studied by deriving an analytical expression for the continuous-time cross-correlation of the transmit signals.  It is shown that, at any spatial point and on any frequency, the received power averaged over many channel realizations from a MIMO base station is the same as from a SISO base station when the two radiate the same amount of power.  For a specific channel realization however, the received power can deviate from this average.  We show that the deviations from the average are small in a MIMO system with multiple users and that the deviations can be significant with only one user.  Using an ergodicity argument, we conclude that out-of-band radiation is less of a problem in massive MIMO, where precoding and array gain let us reduce the total radiated power compared to SISO systems.  The requirements on spectral regrowth can therefore be relaxed in MIMO systems without causing more total out-of-band radiation.

  • 13.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustavsson, Ulf
    Ericsson AB, Sweden.
    Eriksson, Thomas
    Chalmers Univ Technol, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Spatial Characteristics of Distortion Radiated From Antenna Arrays With Transceiver Nonlinearities2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 10, p. 6663-6679Article in journal (Refereed)
    Abstract [en]

    The distortion from massive multiple-input multiple-output base stations with nonlinear amplifiers is studied and its radiation pattern is derived. The distortion is analyzed both in-band and out-of-band. By using an orthogonal Hermite representation of the amplified signal, the spatial cross-correlation matrix of the nonlinear distortion is obtained. It shows that, if the input signal to the amplifiers has a dominant beam, the distortion is beamformed in the same way as that beam. When there are multiple beams without any one being dominant, it is shown that the distortion is practically isotropic. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the out-of-band radiation, to do reciprocity calibration, and to schedule users in the frequency plane to minimize the effect of in-band distortion.

  • 14.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Multiuser MIMO Precoding with Per-Antenna Continuous-Time Constant-Envelope Constraints2015In: 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 (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.

  • 15.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Choi, Junil
    University of Texas at Austin.
    Heath, Robert W.
    University of Texas at Austin.
    Performance of Linear Receivers for Wideband Massive MIMO with One-Bit ADCs2016Conference paper (Refereed)
    Abstract [en]

    The power consumption of analog-to-digital converters (ADCs) grows linearly in the number of antennas in massive MIMO base stations. To reduce power consumption, one-bit ADCs can be used. It is believed that the nonlinear distortion of onebit ADCs makes channel estimation and symbol equalization in such systems computationally complex and resource demanding. In this paper, it is shown that low-complexity linear channel estimation and symbol equalization are feasible in massive MIMO with one-bit ADCs when the number of channel taps is large. The effective SINR of the received symbol estimates of a maximum-ratio combiner with estimated channel state information is 4 dB lower in a system with one-bit ADCs than in an equivalent unquantized system.

  • 16.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Eriksson, Thomas
    Chalmers University of Technology, Gothenburg, Sweden.
    On the Impact of PA-Induced In-Band Distortion in Massive MIMO2014In: Proceedings of European Wireless 2014, Berlin, Offenbach, Germany: VDE Verlag GmbH, 2014, p. 201-206Conference paper (Refereed)
    Abstract [en]

    Conventional downlink signals in massive MIMO suffer from high PAR, which requires the power amplifiers of the base station to be backed off to avoid signal distortion, which lowers power efficiency. To improve efficiency, there are precoding schemes that produce signals with low PAR. To compare different precoding schemes, this article estimates their power consumptions through simulations, in which in-band distortion and amplifier efficiency effects are taken into consideration. It is found that, when only in-band distortion and the data rate requirement determine the back-off, the inband distortion is negligible and the power amplifiers can be operated at peak efficiency. It also turns out that low-PAR and conventional, high-PAR, precoding schemes consume approximately the same amount of power when the out-of-band part of the distortion is disregarded.

  • 17.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Eriksson, Thomas
    Chalmers tekniska högskola, Sweden.
    Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 46, no 12, p. 5050-5063Article in journal (Refereed)
    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.

  • 18.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustavsson, Ulf
    Ericson Res, Sweden.
    Eriksson, Thomas
    Chalmers Univ Technol, Sweden.
    Heath, Robert W. Jr.
    Univ Texas Austin, TX 78712 USA.
    Out-of-Band Radiation from Large Antenna Arrays2018In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 56, no 4, p. 196-203Article in journal (Refereed)
    Abstract [en]

    The OOB radiation from large arrays with nonlinear hardware has a different radiation pattern than the beamformed in-band signal. This is the main difference between the OOB radiation from large arrays and from well-studied legacy systems. Beamforming might focus the OOB radiation in certain directions but also significantly reduce the total power that has to be transmitted. For cost and power-consumption reasons, large arrays might have to be built from low-complexity hardware without advanced pre-compensation for linearization, which increases the relative amount of OOB radiation. Given that large arrays will be used in future base stations, a correct understanding of the OOB radiation is crucial to specify appropriate linearity requirements for the hardware. We show that the OOB radiation from large arrays varies little between coherence times; it is isotropic in many cases; and when it is beamformed, it is directed toward the served user in a very narrow beam with an array gain equal to or less than that of the in-band signal. We draw the conclusion that, compared to legacy systems, less stringent linearity requirements can be used in many systems with large arrays by virtue of the lower transmit power needed to upkeep the same received signal-to-noise ratio.

  • 19.
    Van Chien, Trinh
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Large-scale-fading decoding in cellular Massive MIMO systems with spatially correlated channels2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 4, p. 2746-2762Article in journal (Refereed)
    Abstract [en]

    Massive multiple-input–multiple-output (MIMO) systems can suffer from coherent intercell interference due to the phenomenon of pilot contamination. This paper investigates a two-layer decoding method that mitigates both coherent and non-coherent interference in multi-cell Massive MIMO. To this end, each base station (BS) first estimates the channels to intra-cell users using either minimum mean-squared error (MMSE) or element-wise MMSE estimation based on uplink pilots. The estimates are used for local decoding on each BS followed by a second decoding layer where the BSs cooperate to mitigate inter-cell interference. An uplink achievable spectral efficiency (SE) expression is computed for arbitrary two-layer decoding schemes. A closed form expression is then obtained for correlated Rayleigh fading, maximum-ratio combining, and the proposed large-scale fading decoding (LSFD) in the second layer. We also formulate a sum SE maximization problem with both the data power and LSFD vectors as optimization variables. Since this is an NP-hard problem, we develop a low-complexity algorithm based on the weighted MMSE approach to obtain a local optimum. The numerical results show that both data power control and LSFD improve the sum SE performance over single-layer decoding multi-cell Massive MIMO systems.

  • 20.
    Van Chien, Trinh
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollén, Christopher
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Two-Layer Decoding in Cellular Massive MIMO Systems with Spatial Channel Correlation2019Conference paper (Refereed)
    Abstract [en]

    This paper studies a two-layer decoding method that mitigates inter-cell interference in multi-cell Massive MIMO systems. In layer one, each base station (BS) estimates the channels to intra-cell users and uses the estimates for local decoding on each BS, followed by a second decoding layer where the BSs cooperate to mitigate inter-cell interference. An uplink achievable spectral efficiency (SE) expression is computed for arbitrary two-layer decoding schemes, while a closed-form expression is obtained for correlated Rayleigh fading channels, maximum-ratio combining (MRC), and large-scale fading decoding (LSFD) in the second layer. We formulate a non-convex sum SE maximization problem with both the data power and LSFD vectors as optimization variables and develop an algorithm based on the weighted MMSE (minimum mean square error) approach to obtain a stationary point with low computational complexity.

1 - 20 of 20
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf