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Spectrally Precoded OFDM-Design and Analysis
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0002-9225-8150
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Spektral förkodning i OFDM-design och analys (Swedish)
Abstract [en]

Despite shifting towards mm-wave bands, the sub-6 GHz band will continue to be a fundamental spectral band in 5G. However, the severe congestion in this band makes a well-constrained spectrum a critical requirementof 5G. A well-constrained spectrum means that the communications regimes should dwell within their dedicated spectral bands and do not interfere with other systems working on neighboring bands. Consequently, the communi-cations community seeks convenient modulation schemes.

The 5G standards have already defined cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) as the modulation scheme for most of the sub-6 GHz band. However, the high out-of-band (OOB) emission phe-nomenon in OFDM is unfavorable for some regimes operating in 5G. Therefore, to legitimize OFDM in all 5G regimes, we need to suppress the OFDM OOB emission.

Since the discontinuous nature of the OFDM signal is the main reason forthe high OOB emission, one solution is to render the discontinuous OFDM signal continuous. Two factors control this discontinuity: the physical shape of the modulated signal and the correlation of the data symbols that modulate the OFDM signal.

While most traditional approaches focus on reshaping the OFDM signal to render it continuous, in this work, we give our attention to the spectral precoding approaches. These approaches manipulate the correlation of the data symbols to control the high OOB emission in OFDM.

After almost ten years of analytical and theoretical study of the spectralprecoding approaches in the literature, we believe it is time to investigate the practicality and ability of spectral precoding methods to compete with traditional approaches. Consequently, we check whether spectral precoding satisfies the spectral requirements of LTE measures. We analyze the precoders' implementation complexity and provide methodologies to reduce it. We design practical spectral precoders that match with the practical OFDM transmitters, and we study spectral precoding extensibility toward MIMO (and massive MIMO) systems.

Moreover, in this work, we introduce the first proof-of-concept prototype of spectrally precoded OFDM. In the prototype, we use software-defined radios (SDRs) to perform a real-time examination of how spectral precoding improves the spectral containment of OFDM systems.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
OFDM, spectral precoding, out of band emission, 5G
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
URN: urn:nbn:se:ltu:diva-71971ISBN: 978-91-7790-282-9 (print)ISBN: 978-91-7790-283-6 (electronic)OAI: oai:DiVA.org:ltu-71971DiVA, id: diva2:1269045
Public defence
2019-02-19, E632, Luleå tekniska universitet, Luleå, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilAvailable from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-01-31Bibliographically approved
List of papers
1. An analysis of out-of-band emission and in-band interference for precoded and classical OFDM systems
Open this publication in new window or tab >>An analysis of out-of-band emission and in-band interference for precoded and classical OFDM systems
2015 (English)In: European Wireless 2015: 21th European Wireless Conference, 20-22 May 2015, Budapest, Hungary, Piscataway, NJ: IEEE Communications Society, 2015, article id 7147703Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we present analytical expressions for the out-of-band (OOB) emission and in-band interference of two different OOB suppressed OFDM-systems; classical low-pass filtered and precoded. Then, we analytically compare their performance in terms of OOB emission suppression and introduced level of in-band interference. We analyse the fact that the in-band interference introduced by the filter depends on the length of the cyclic prefix as well as the behavior of the channel while that of the precoded OFDM does not. The analysis confirms that edged subcarriers suffer higher in-band interference than central subcarriers. Moreover, frequency precoders, for a specific choice of notching frequencies, can outperform time precoders.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Communications Society, 2015
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-34467 (URN)8ad284fe-4be4-4f35-b93d-3e81a90f5fb2 (Local ID)978-3-8007-3976-9 (ISBN)8ad284fe-4be4-4f35-b93d-3e81a90f5fb2 (Archive number)8ad284fe-4be4-4f35-b93d-3e81a90f5fb2 (OAI)
Conference
European Wireless : 20/05/2015 - 22/05/2015
Note
Godkänd; 2015; 20150703 (jaavan)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-12-07Bibliographically approved
2. Minimum-EVM N-continuous OFDM
Open this publication in new window or tab >>Minimum-EVM N-continuous OFDM
2016 (English)In: 2016 IEEE International Conference on Communications (ICC): Kuala Lumpur, 22-27 May 2016, Piscataway, NJ: IEEE Communications Society, 2016, article id 7511164Conference paper, Published paper (Refereed)
Abstract [en]

The N-continuous precoder for the suppression ofOOB emission in OFDM systems that minimizes the EVM isintroduced. We show that the minimum in-band interference dueto the introduced precoding approach is 3 dB less than the inbandinterference of existing N-continuous precoders. Moreover,we introduce a novel practical block precoder that approachesthe performance of the suggested optimal precoder. We analyzethe spectrum of the OFDM signal after block precoding, the inbandinterference due to block precoding and the effect of blockprecoding on the BER. The price to pay for block precoding isthe computational complexity that grows linearly with the blocksize.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Communications Society, 2016
Keywords
OFDM, spectrum, out of band emission, in-band interference, Information technology - Signal processing, Informationsteknik - Signalbehandling
National Category
Signal Processing
Research subject
Signal Processing; Enabling ICT (AERI)
Identifiers
urn:nbn:se:ltu:diva-31163 (URN)10.1109/ICC.2016.7511164 (DOI)000390993203035 ()2-s2.0-84981306982 (Scopus ID)54014940-6cf4-4e51-974e-dcfdcf2fed88 (Local ID)978-1-4799-6664-6 (ISBN)54014940-6cf4-4e51-974e-dcfdcf2fed88 (Archive number)54014940-6cf4-4e51-974e-dcfdcf2fed88 (OAI)
Conference
IEEE International Conference on Communications : 23/05/2016 - 27/05/2016
Note

Godkänd; 2016; 20151105 (jaavan)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-12-07Bibliographically approved
3. An SDR-based prototype of spectrally-precoded OFDM
Open this publication in new window or tab >>An SDR-based prototype of spectrally-precoded OFDM
2017 (English)In: EuCNC 2017: European Conference on Networks and Communications, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980758Conference paper, Published paper (Refereed)
Abstract [en]

Spectrally precoded OFDM is a recent approach that aims for the suppression of the OOB, as well as the in-band gap, emissions in OFDM systems. Theoretically, the technique shows High suppression of the OOB and the in-band gap emissions. Although, practically hardware impairments may limit the precoder's performance. Yet, this demonstration shows that despite the hardware impairments, implemented spectrally precoded OFDM generates emissions tens of decibels less than that of plain OFDM. Therefore, the demonstration proves that communications links are less vulnerable to interference coming from spectrally precoded OFDM signals than to interference coming from plain OFDM signals

Place, publisher, year, edition, pages
Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-64716 (URN)10.1109/EuCNC.2017.7980758 (DOI)000425922900118 ()2-s2.0-85039935034 (Scopus ID)978-1-5386-3873-6 (ISBN)
Conference
European Conference on Networks and Communications (EuCNC 2017), Oulu, Finland, 12-15 June 2017
Available from: 2017-07-01 Created: 2017-07-01 Last updated: 2018-12-07Bibliographically approved
4. A Novel Transmitter Architecture for Spectrally-Precoded OFDM
Open this publication in new window or tab >>A Novel Transmitter Architecture for Spectrally-Precoded OFDM
2018 (English)In: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 65, no 8, p. 2592-2605Article in journal (Refereed) Published
Abstract [en]

Frequency nulling spectral precoding is an approachthat suppresses the out-of-band emission in OFDM systems.In this paper, we discuss the transmitter architecture of thespectrally precoded OFDM systems. We design a novel precoderthat matches the practical implementation of the OFDM modulator.We show that spectral precoding can relax the analog lowpass filtering requirements of the OFDM system transmitter. Weexamine the effect of spectral precoding on the PAPR as wellas the effect of the PA on the spectral precoding suppressionperformance. We also study the compliance of the spectrallyprecoded OFDM transmitter with the 3GPP standardizationmeasures and analyze its computation complexity. At the receiverside, we analyze the in-band interference and BER performanceof the suggested precoding approach.

Place, publisher, year, edition, pages
IEEE, 2018
National Category
Engineering and Technology Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-67847 (URN)10.1109/TCSI.2018.2797527 (DOI)000437882000022 ()2-s2.0-85041808007 (Scopus ID)
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning
Note

Validerad;2018;Nivå 2;2018-08-08 (rokbeg)

Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2018-12-07Bibliographically approved
5. N-smooth OFDM
Open this publication in new window or tab >>N-smooth OFDM
(English)In: Article in journal, Letter (Refereed) Submitted
Abstract [en]

This paper introduces a new multicarrier system - a practical alternative for N-continuous OFDM: N-smooth OFDM. N-smooth OFDM improves the spectral compactness of practical OFDM systems by suppressing OOB emission. The higher spectral compactness of N-smooth OFDM allows the system to relax requirements of the digital to analog converter (DAC) construction filter. Moreover, it decreases the signal's self interference that results from spectral precoding as well as precoder's computational complexity. 

Keywords
OFDM, Signals, Spectral precoding, OOB
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-71966 (URN)
Funder
Swedish Research Council
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07
6. Joint spectral-spatial precoders in massive-MIMO OFDM transmitters
Open this publication in new window or tab >>Joint spectral-spatial precoders in massive-MIMO OFDM transmitters
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

In this paper we propose novel joint spectral-spatial precoders for large-antennaOFDM systems that suppress both spatial multi-user interference and spectral out-ofbandpower emissions. We analyse the performance of the proposed precoder in termsof spectral characteristics, system sum-rate and transmitter complexity. We show inparticular that, interestingly, the proposed joint maximum-ratio precoder has a simpletransmitter structure of two separate and consecutive banks of spectral and spatialprecoders.

National Category
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-71967 (URN)
Funder
Swedish Research Council
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07
7. Subspace-precoded OFDM with low Out-of-Band Emissions:it will work
Open this publication in new window or tab >>Subspace-precoded OFDM with low Out-of-Band Emissions:it will work
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Today’s multicarrier transmitters, deployed in essentially all communications radio equipment we use(phones, TV’s, computers, etc.), contain means to avoid undesired out-of-band power emissions. Standards and regulations typically restrict the levels of these emissions in order to allow for an efficient use of the radio spectrum. Radio vendors deploy well-established algorithms such as low-pass filtering or windowing to satisfy these regulations. A new approach, specifically applicable to OFDM systems, known as spectralprecoding, has been studied during the last decade. In particular, subspace precoding has attracted theinterest of academia, for its elegance, and despite a few adamant disadvantages. Recent advances now provide a breakthrough: subspace precoding is now a viable alternative to today’s algorithms.

National Category
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-71969 (URN)
Funder
Swedish Research Council
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07

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