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Joint spectral-spatial precoders in MIMO-OFDM transmitters
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0003-1711-8606
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0002-9225-8150
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0003-0413-4826
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0001-8647-436x
2020 (English)In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557Article in journal (Refereed) Epub ahead of print
Abstract [en]

This work studies the joint design of spectral precoding, to avoid spectral out-of-band power emissions, and spatial precoding, to suppress spatial multiuser interference, in MIMO-OFDM systems. In current state-of-art approaches the transmit signals are precoded using two independently designed spectral and spatial precoders. In contrast this paper proposes a joint precoding of the signal to achieve a better performance. We analyse the performance of the proposed precoder in terms of spectral characteristics, system spectral efficiency and transmitter complexity. We show in particular that, interestingly, the proposed joint maximum-ratio precoder has a simple transmitter structure of two separate and consecutive banks of spectral and spatial precoders which in fact can be designed independently, while in case of zero-forcing the off-the-shelf precoders are far from the optimal. The joint zero-forcing precoder has a coupled structure and hence, we can not decompose it.

Place, publisher, year, edition, pages
2020.
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
URN: urn:nbn:se:ltu:diva-77829DOI: 10.1016/j.sigpro.2020.107538Scopus ID: 2-s2.0-85080054992OAI: oai:DiVA.org:ltu-77829DiVA, id: diva2:1395701
Funder
Swedish Research CouncilAvailable from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-04-22
In thesis
1. Spectrally Precoded OFDM-Design and Analysis
Open this publication in new window or tab >>Spectrally Precoded OFDM-Design and Analysis
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Spektral förkodning i OFDM-design och analys
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
OFDM, spectral precoding, out of band emission, 5G
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-71971 (URN)978-91-7790-282-9 (ISBN)978-91-7790-283-6 (ISBN)
Public defence
2019-02-19, E632, Luleå tekniska universitet, Luleå, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2020-04-22Bibliographically approved

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Taheri, TayebehMohamad, MedhatNilsson, RickardBeek, Jaap van de

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