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Mohamad, M. (2019). Spectrally Precoded OFDM-Design and Analysis. (Doctoral dissertation). Luleå: Luleå University of Technology
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: 2019-01-31Bibliographically approved
Mohamad, M., Nilsson, R. & Beek, J. v. (2018). A Novel Transmitter Architecture for Spectrally-Precoded OFDM. IEEE Transactions on Circuits and Systems Part 1: Regular Papers, 65(8), 2592-2605
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
Carlson, J. E., Andren, E., Mohamad, M. & Beek, J. v. (2018). Monitoring Changes in Mechanical Properties of Rock Bolts Using a Low-Power Coded-Excitation Scheme. In: 2018 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS): . Paper presented at 2018 IEEE International Ultrasonics Symposium, IUS 2018; Kobe; Japan; 22-25 Oct 2018. IEEE, Article ID 8580038.
Open this publication in new window or tab >>Monitoring Changes in Mechanical Properties of Rock Bolts Using a Low-Power Coded-Excitation Scheme
2018 (English)In: 2018 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), IEEE, 2018, article id 8580038Conference paper, Published paper (Refereed)
Abstract [en]

In-situ inspection and quality assessment of rock bolts and other load-bearing structural elements, has received significant attention over the years, but there are still no techniques available capable of monitoring changes over time in mechanical properties of already installed bolts. Since mechanical changes will also affect the propagation of mechanical waves, ultrasound is a strong candidate. In this paper we propose a technique based on Orthogonal Frequency Division Multiplexing (OFDM) for coding the transmitted ultrasound pulse in such a way that the propagation channel (transducer and rock bolt combined) can be estimated. We show that a transmit voltage of 1.1 V r.m.s. is sufficient to obtain reliable channel estimates even in bolts as long as one meter. The channel estimates are then used to predict changes in tensile stress on the bolt, from experiments conducted in a laboratory environment.

Place, publisher, year, edition, pages
IEEE, 2018
Series
IEEE International Ultrasonics Symposium, ISSN 1948-5719, E-ISSN 48-5727
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-72802 (URN)10.1109/ULTSYM.2018.8580038 (DOI)000458693001081 ()2-s2.0-85060589109 (Scopus ID)978-1-5386-3425-7 (ISBN)978-1-5386-3426-4 (ISBN)
Conference
2018 IEEE International Ultrasonics Symposium, IUS 2018; Kobe; Japan; 22-25 Oct 2018
Available from: 2019-02-06 Created: 2019-02-06 Last updated: 2019-03-11Bibliographically approved
Mohamad, M., Nilsson, R. & van de Beek, J. (2017). An SDR-based prototype of spectrally-precoded OFDM. In: EuCNC 2017: European Conference on Networks and Communications. Paper presented at European Conference on Networks and Communications (EuCNC 2017), Oulu, Finland, 12-15 June 2017. Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), Article ID 7980758.
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
Carlson, J., van de Beek, J. & Mohamad, M. (2017). Mbit/second Communication through a Rock Bolt Using Ultrasound. In: : . Paper presented at 2017 IEEE International Ultrasonics Symposium (IUS), Washington D.C., 6-9 Sept. 2017. Piscataway, NJ: IEEE, Article ID 8092454.
Open this publication in new window or tab >>Mbit/second Communication through a Rock Bolt Using Ultrasound
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

In most industrial processes transfer of data and software from or to sensors is an essential part of the monitoring and control systems. Many of the older, wired communication systems have been or are being replaced with wireless alternatives. A number of challenges are associated with this replacement: Radio receivers are subject to interference from other radio sources. Similarly, radio transmitters may cause undesired interference into other equipment and environments. Compared to wired solutions, security becomes an issue as radio communication links are more vulnerable to eavesdropping than wired schemes. Radio communication with sensors and sensor platforms embedded deep inside large metal structures or fluid tanks may be difficult or even impossible. The objective of this work is to develop and evaluate a high data-rate communications scheme based on ultrasound, which can be used to transmit wirelessly through solid structures. An example will be given using a one-meter segment of a rock bolt.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE, 2017
Series
IEEE International Ultrasonics Symposium, ISSN 1948-5719, E-ISSN 1948-5727
Keywords
Ultrasonic imaging, Rocks, Fasteners, Sensors, Radio communication, Interference, Channel estimation
National Category
Signal Processing Telecommunications
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-66541 (URN)10.1109/ULTSYM.2017.8092454 (DOI)2-s2.0-85039419149 (Scopus ID)978-1-5386-3383-0 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium (IUS), Washington D.C., 6-9 Sept. 2017
Available from: 2017-11-10 Created: 2017-11-10 Last updated: 2018-12-07Bibliographically approved
Carlson, J., van de Beek, J. & Mohamad, M. (2017). Mbit/second Communication through a Rock Bolt Using Ultrasound. In: IEEE International Ultrasonics Symposium, IUS: . Paper presented at 2017 IEEE International Ultrasonics Symposium (IUS), Washington D.C., 6-9 Sept. 2017. Piscataway, NJ: IEEE Computer Society, Article ID 8092474.
Open this publication in new window or tab >>Mbit/second Communication through a Rock Bolt Using Ultrasound
2017 (English)In: IEEE International Ultrasonics Symposium, IUS, Piscataway, NJ: IEEE Computer Society, 2017, article id 8092474Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a digital communication system based on Orthogonal Frequency Division Multiplexing (OFDM) and MHz-range ultrasound, for transmission of data through solid materials and liquids. The system is tested on experiments using a off-the-shelf ultrasound transducers with a center frequency of 3.5 MHz as transmitter and receiver, respectively. The propagation medium in the experiment was a 1 m long section of an epoxy coated steel rock bolt. The results show that data rates in excess of 1 Mbit/second is attainable, using readily available hardware and software.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Computer Society, 2017
Series
IEEE International Ultrasonics Symposium, ISSN 1948-5719, E-ISSN 1948-5727
National Category
Signal Processing Telecommunications
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-65477 (URN)10.1109/ULTSYM.2017.8092474 (DOI)000416948402010 ()978-1-5386-3383-0 (ISBN)978-1-5386-3384-7 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium (IUS), Washington D.C., 6-9 Sept. 2017
Available from: 2017-09-04 Created: 2017-09-04 Last updated: 2018-12-07Bibliographically approved
Mohamad, M. (2016). Activity: An SDR-based prototype of spectrally precoded OFDM (ed.). Paper presented at EAI International Conference on Cognitive Radio Oriented Wireless Networks : 30/05/2016 - 01/06/2016. Paper presented at EAI International Conference on Cognitive Radio Oriented Wireless Networks : 30/05/2016 - 01/06/2016.
Open this publication in new window or tab >>Activity: An SDR-based prototype of spectrally precoded OFDM
2016 (English)Conference paper, Published paper (Other (popular science, discussion, etc.))
Abstract [en]

OFDM scheme possesses high OOB emission which degrades the spectral efficiency of OFDM systems. Poor spectral efficiency limits the validity of OFDM as a candidate for 5G. Spectrally precoded OFDM is a recent approach that treats the OFDM signal to suppress the out of band (OOB) emission. Although the theoretical results of spectral precoding show very efficient OOB emission suppression (more than 50 dB reduction compared to plain OFDM), practically, hardware impairments limit its performance.We, at Luleå University of Technology, examine the practicality of the suggested approach and show for the first time through this demonstration that despite the hardware impairments, implemented spectral precoded OFDM has OOB emission tens of decibels less than that of plain OFDM. We set up and examine a communication link through which we approve that communication systems are less vulnerable to interference coming from spectrally precoded OFDM signals than to interference coming from plain OFDM signals.

National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-41637 (URN)9828426f-1a40-4797-9902-be74b3887b22 (Local ID)9828426f-1a40-4797-9902-be74b3887b22 (Archive number)9828426f-1a40-4797-9902-be74b3887b22 (OAI)
Conference
EAI International Conference on Cognitive Radio Oriented Wireless Networks : 30/05/2016 - 01/06/2016
Note
Startdatum: 30/05/2016; Slutdatum: 01/06/2016; Roll: Annat; Typ: Föreläsning / muntligt bidragAvailable from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-12-08Bibliographically approved
Mohamad, M. (2016). Design, Analysis and Prototyping of Spectrally Precoded OFDM. (Licentiate dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>Design, Analysis and Prototyping of Spectrally Precoded OFDM
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Despite shifting towards mm-wave bands, the sub 6-GHz band will continue tobe a fundamental spectral band in 5G. Yet, the severe crowdedness of this bandmakes a well constrained spectrum one of the critical 5G requirements. A wellconstrained spectrum means that the communications regimes should dwell politelywithin their dedicated spectral bands and not interfere with other systems workingon neighboring bands. Consequently, communications community seeks convenientmodulation schemes.Accordingly, high Out Of Band (OOB) emission phenomenon in Orthogonal Fre-quency Division Multiplexing (OFDM) is unfavorable for some regimes operating in5G. Therefore, to legitimize OFDM with all 5G regimes, we need to suppress OFDMOOB emission.Since the discontinuous nature of the OFDM signal is the main reason for the highOOB emission, one solution is to render the discontinuous OFDM signal continuous.Two factors control this discontinuity: the physical shape of the modulated signaland the correlation property of the data symbols that modulate the OFDM signal.While most of the traditional approaches focus on reshaping the OFDM signalto render it continuous, in this work we give our attention to the spectral precod-ing approaches. These approaches manipulate the correlation property of the datasymbols to control the high OOB emission in OFDM.On the other hand, tweaking the correlation property of the modulating datasymbols will violate their orthogonality. This violation will yield in-band interfer-ence within the OFDM signal which would degrade the bit error performance of thereceived data.The thesis explains the spectral precoding techniques from conceptual and math-ematical point of view. We discuss the OOB emission suppression capability of theprecoding techniques and study their drawbacks and limitations. We provide ana-lytical trade o study between precoding approaches and classical OFDM treatmentapproaches at the level of OOB emission suppression and in-band interference. Weshow that the in-band interference in precoding techniques is independent on thecommunications channel behavior contrary to that of classical techniques. More-over, we dene the optimal precoder that minimizes the in-band interference. Con-sequently, we design a novel practical precoder that approaches the performanceof the optimal precoder. Furthermore, we analyze the complexity of the precodingapproaches and study the implementation computational requirements.Finally, we test the real time performance of these precoding techniques usingSoftware Designed Radio (SDR) Universal Software Radio Peripherals (USRPs). Wespotlight the hardware limitations and show that despite these limitations, the spec-tral precoder is able to suppress the OOB emissions by tens of decibels. We check the reliability of spectral precoding in practical over air communications systems bysetting up the rst spectral precoding proof of concept prototype. The prototypeproves that precoded OFDM systems cause less OOB interference on neighboringcommunications systems.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2016
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-139 (URN)978-91-7583-680-5 (ISBN)978-91-7583-681-2 (ISBN)
Presentation
2016-10-20, A3024, Luleå tekniska universitet, Luleå, 13:00
Opponent
Supervisors
Available from: 2016-09-15 Created: 2016-09-15 Last updated: 2019-01-30Bibliographically approved
Mohamad, M., Nilsson, R. & Beek, J. v. (2016). Minimum-EVM N-continuous OFDM (ed.). In: (Ed.), 2016 IEEE International Conference on Communications (ICC): Kuala Lumpur, 22-27 May 2016. Paper presented at IEEE International Conference on Communications : 23/05/2016 - 27/05/2016. Piscataway, NJ: IEEE Communications Society, Article ID 7511164.
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
Mohamad, M., Nilsson, R. & Beek, J. v. (2015). An analysis of out-of-band emission and in-band interference for precoded and classical OFDM systems (ed.). In: (Ed.), (Ed.), European Wireless 2015: 21th European Wireless Conference, 20-22 May 2015, Budapest, Hungary. Paper presented at European Wireless : 20/05/2015 - 22/05/2015. Piscataway, NJ: IEEE Communications Society, Article ID 7147703.
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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9225-8150

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