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Nader, Charles
Publications (10 of 21) Show all publications
Nader, C. (2014). The True Value of a PhD in the Eyes of Industry. IEEE Instrumentation & Measurement Magazine, 17(5), 24-25
Open this publication in new window or tab >>The True Value of a PhD in the Eyes of Industry
2014 (English)In: IEEE Instrumentation & Measurement Magazine, ISSN 1094-6969, E-ISSN 1941-0123, Vol. 17, no 5, p. 24-25Article in journal, Editorial material (Other academic) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hig:diva-18311 (URN)10.1109/MIM.2014.6912197 (DOI)000343703400006 ()
Available from: 2014-12-09 Created: 2014-12-09 Last updated: 2018-03-13Bibliographically approved
Nader, C., Van Moer, W., Björsell, N. & Händel, P. (2013). Wideband Radio Frequency Measurements: From Instrumentation to Sampling Theory. IEEE Microwave Magazine, 14(2), 85-98
Open this publication in new window or tab >>Wideband Radio Frequency Measurements: From Instrumentation to Sampling Theory
2013 (English)In: IEEE Microwave Magazine, ISSN 1527-3342, E-ISSN 1557-9581, Vol. 14, no 2, p. 85-98Article in journal (Refereed) Published
Abstract [en]

Whether listening to broadcast radio or testing developed wireless devices, for civilian or military applications, based on terrestrial or spatial links, a radio frequency (RF) receiver with good measurement capabilities that preserves the received signal information is required. Todays RF measurement receivers with wideband capabilities are split into two groups based on the measurement strategy they adopt. Both groups produce a time domain waveform with both amplitude and phase information that is constructed either from a transformation of its frequency contents or directly from its time-domain samples.

Keywords
Radio frequency, Receivers, Time domain analysis, Time frequency analysis, Wideband
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-13977 (URN)10.1109/MMM.2012.2234643 (DOI)000316261800010 ()2-s2.0-84874983510 (Scopus ID)
Available from: 2013-09-16 Created: 2013-03-20 Last updated: 2019-12-11Bibliographically approved
Nader, C., Landin, P. N., Van Moer, W., Björsell, N., Händel, P. & Rönnow, D. (2012). Peak-power Controlling Technique for Enhancing Digital Pre-distortion of RF Power Amplifiers. IEEE transactions on microwave theory and techniques, 60(11), 3571-3581
Open this publication in new window or tab >>Peak-power Controlling Technique for Enhancing Digital Pre-distortion of RF Power Amplifiers
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2012 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 60, no 11, p. 3571-3581Article in journal (Refereed) Published
Abstract [en]

In this paper, we present a method to limit the generation of signal peak power at the output of a digital pre-distorter that is applied to a RF power amplifier (PA) operating in strong compression. The method can be considered as a joint crest-factor reduction and digital pre-distortion (DPD). A challenging characteristic of DPD when applied to a PA in strong compression is the generation of relatively high peaks due to the DPD expansion behavior. Such high peaks generation, which may be physically unrealistic, can easily damage the amplification system. Such a phenomenon, referred in this study as DPD-avalanche, is more noticed when the signal exciting the PA is compressed due to crest-factor reduction. The suggested method for controlling such DPD-avalanche is based on shaping the input signal to the DPD in such a way to keep the pre-distorted signal peak power below or near the maximum allowed peak power of the PA. The suggested method is tested experimentally on a Class-AB and a Doherty PA when excited with a wideband orthogonal frequency-division multiplexing (OFDM) signal. Scenarios for an OFDM signal with and without crest-factor reduction are evaluated. Measurement results when using the proposed DPD-avalanche controller show smooth deterioration of the in-band and out-of-band linearity compared to steep deterioration when no controller is used. In addition, the suggested controller offers a higher operating power range of the DPD while fulfilling out-of-band distortion requirements and preserving low in-band error.

National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-12655 (URN)10.1109/TMTT.2012.2213836 (DOI)000310969100025 ()2-s2.0-84869380701 (Scopus ID)
Available from: 2012-08-23 Created: 2012-08-23 Last updated: 2019-12-11Bibliographically approved
Nader, C., Van Moer, W., Björsell, N., Barbé, K. & Händel, P. (2012). Reducing The Analog and Digital Bandwidth Requirements of RF Receivers for Measuring Periodic Sparse Waveforms. IEEE Transactions on Instrumentation and Measurement, 61(11), 2960-2971
Open this publication in new window or tab >>Reducing The Analog and Digital Bandwidth Requirements of RF Receivers for Measuring Periodic Sparse Waveforms
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2012 (English)In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 61, no 11, p. 2960-2971Article in journal (Refereed) Published
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-12654 (URN)10.1109/TIM.2012.2203729 (DOI)000309866500013 ()2-s2.0-84867576623 (Scopus ID)
Available from: 2012-08-23 Created: 2012-08-23 Last updated: 2019-12-11Bibliographically approved
Van Moer, W., Björsell, N., Hamid, M., Barbe, K. & Nader, C. (2012). Saving lives by integrating cognitive radios into ambulances. In: Medical Measurements and Applications Proceedings (MeMeA), 2012 IEEE International Symposium on. Paper presented at Medical Measurements and Applications Proceedings (MeMeA), 18-19 May 2012, Budapest (pp. 1-4). Budapest
Open this publication in new window or tab >>Saving lives by integrating cognitive radios into ambulances
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2012 (English)In: Medical Measurements and Applications Proceedings (MeMeA), 2012 IEEE International Symposium on, Budapest, 2012, p. 1-4Conference paper, Published paper (Refereed)
Abstract [en]

A brain stroke is defined as a disturbance in the blood supply of the brain. This can be due to either an obstruction in the blood vessels of the brain or a rupture in the blood vessels which causes a leakage of blood in the brain. In many cases, a stroke results in the death of the patient within 24 hours. Hence, it is crucial that the neurologist has immediately contact with the patient in the first 30 minutes after the stroke. This means that a direct broadband communication link between the ambulance and the hospital is needed in order to transmit all necessary physiological parameters, such as blood pressure and glucose level as well as video images. In this paper, we present a new architecture of a wireless communication link between the ambulance and the hospital based on the concept of cognitive radios. The sender/receiver module in the ambulance will allow measuring the wideband spectrum and search for a suitable empty frequency band to send the data.

Place, publisher, year, edition, pages
Budapest: , 2012
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-12700 (URN)10.1109/MeMeA.2012.6226619 (DOI)2-s2.0-84864184682 (Scopus ID)978-1-4673-0880-9 (ISBN)
Conference
Medical Measurements and Applications Proceedings (MeMeA), 18-19 May 2012, Budapest
Available from: 2012-08-28 Created: 2012-08-28 Last updated: 2019-12-11Bibliographically approved
Nader, C. (2012). Signal Shaping and Sampling-based Measurement Techniques for Improved Radio Frequency Systems. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Signal Shaping and Sampling-based Measurement Techniques for Improved Radio Frequency Systems
2012 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

Wireless communication systems are omnipresent in our day-to-day life, with high expectations regarding capacity, reliability and power efficiency. In order to satisfy the capacity and reliability expectations, today's wireless systems are adopting sophisticated modulation schemes, such as orthogonal frequency division multiplexing (OFDM), which shape today's wireless signals with large bandwidths and high crest factors. On top of that, it is anticipated that different wireless systems/standards will co-exist and share the same radio frequency (RF) front-end in order to reduce the network implementation cost.

  Such signals characteristics and systems coexistence put high requirements on the amplification stage which in best scenarios is considered weakly nonlinear. As a result, the power amplifier needs to be backed-off for linear operation. However, such power back-off reduces the operation's efficiency. Reducing the crest factor of the wireless signal and the possibility to linearize by means of digital pre-distortion the operation behavior of the power amplifier when operated near its maximum allowed continuous wave (CW) operating power range would lead to the optimal linearity and efficiency of operation.

  In order to achieve a good linearization performance, accurate baseband behavioral models are needed which requires measuring time domain signals whose spectra spread largely due to the nonlinear operation of the power amplifier. Such spectrum spreading, denoted by spectral regrowth, puts high requirements on today's sampling-based measurement systems as a trade-of between the sampling rate and amplitude resolution exists in today's generation of analog-to-digital converters, in addition to a limitation in the available analog bandwidth. Overcoming such measurement challenges could lead to the design of expensive measurement systems which is not favorable.

  In this thesis, the performance of RF transmitters is improved by combining the use of a smart crest factor reduction technique with an enhanced digital pre-distortion technique which allows operating the power amplifier near its CW 1-dB compression point, offering a significant increase in the efficiency of operation while satisfying the standard constraints on information error and spectral emission. Furthermore, the performance of RF measurement receivers is improved by reducing the requirements on the digital bandwidth by means of an evolved harmonic sampling technique, and by reducing the requirements on the analog bandwidth and design cost by means of a digital bandwidth interleaving technique and a signal separation technique based on an advanced sparse reconstruction methodology.

Abstract [sv]

Trådlösa kommunikationssystem förekommer överallt i vår vardag, med höga förväntningar på kapacitet, tillförlitlighet och energieffektivitet. För att uppfylla förväntningar på kapacitet och tillförlitlighet är dagens trådlösa system utrustade med avancerade modulationsmetoder, såsom Orthogonal Frequency Division Multiplexing (OFDM), vilket medför att dagens trådlösa signaler har stora bandbredder och höga toppfaktorer. Därutöver planeras det för att olika trådlösa system/standarder kommer att samexistera och samutnyttja komponenter i gränssnittet mot radiosignaler, s.k. RF front-end, för att därigenom minska kostnader för nätverk.

Egenskaperna hos dessa signaler och samexisterande system ställer höga krav på förstärkarsteg som i bästa fall kan anses svagt olinjära. Som ett resultat av detta behöver effektförstärkaren arbetspunkt flyttas för förstärkaren skall arbeta i det linjära området, men en sådan förflyttning minskar systemets verkningsgrad. Genom att reducera toppfaktorn på den trådlösa signalen samt att linjärisera förstärkarsteget genom digital förförvrängning, även kallad predistortion, hos effektförstärkaren när den drivs nära sin högsta tillåtna arbetspunkt för en kontinuerlig signal (CW) kan optimal linjäritet och effektiv drift erhållas.

För att uppnå god linjäriseringsprestanda krävs noggranna modeller som beskriver beteende i basbandet. Att ta fram dessa modeller kräver tidsdomänmätningar av signaler vars spektra är bredbandiga, till stor del beroende på icke-linjär drift av effektförstärkaren. Bredbandiga spektra ställer höga krav på dagens samplande mätsystem i och med kompromissen mellan samplingsfrekvens och upplösning i amplitud finns i dagens generation av analog till digital omvandlare; dessutom finns en begränsning i tillgänglig analog bandbredd. Att lösa dessa utmanande mätproblem kan leda till utformning av dyra mätsystem vilket inte är önskvärt.

I denna avhandling förbättras prestandan hos en radiosändare genom en kombination av smart toppfaktorreduktion och förbättrad digital predistortionsteknik som gör det möjligt att driva effektförstärkaren nära sin 1 dB kompressionspunkt, vilket erbjuder en betydande ökning av systemets verkningsgrad samtidigt som det uppfyller standarders krav avseende vektornoggrannhet och spektral spridning. Dessutom har prestandan på mätutrustningen för radiofrekvenser (RF) förbättras genom att minska kraven på digital bandbredd med hjälp av en nyutvecklad harmonisk samplingsteknik, och genom att minska kraven på den analoga bandbredden och konstruktionskostnad med hjälp av en teknik att intersekvensera signaler i den digitala frekvensdomänen samt med en signalseparationsteknik baserad på en avancerad rekonstruktionsmetod för glesa signaler.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. p. xix, 204
Series
TRITA-EE, ISSN 1653-5146 ; 2012:026
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-18697 (URN)978-91-7501-422-7 (ISBN)
Public defence
2012-08-17, Hörsal 99:131, Högskolan i Gävle, Kungsbäcksvägen 47, 13:00 (English)
Opponent
Supervisors
Available from: 2015-01-09 Created: 2015-01-09 Last updated: 2018-03-13Bibliographically approved
Nader, C., Van Moer, W., Barbé, K., Björsell, N. & Händel, P. (2011). Characterizing the out-of-band nonlinear behaviour of RF devices: the key to success. In: 2011 IEEE International Instrumentation and Measurement Technology Conference (I2MTC): . Paper presented at 2011 IEEE International Instrumentation and Measurement Technology Conference I2MTC, Hangzhou, China, 10-12 May 2011 (pp. 790-794). New York: IEEE conference proceedings
Open this publication in new window or tab >>Characterizing the out-of-band nonlinear behaviour of RF devices: the key to success
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2011 (English)In: 2011 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), New York: IEEE conference proceedings, 2011, p. 790-794Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a measurement recipe to characterize the out-of-band nonlinear behavior of RF devices when harmonic sampling is used as a digitizing technique. A major challenge to consider when using harmonic sampling is the overlapping of the aliased spectral bins of the digitized waveform. This challenge is more pronounced when using modulated excitation signals. In addition, the excitation signal used should mimic the real behavior of signals used in today's wireless systems. Hence, this paper provides the reader with a tool to select the proper excitation signal, sampling frequency and record length in order to achieve an accurate characterization of the nonlinear behavior of RF devices.

Place, publisher, year, edition, pages
New York: IEEE conference proceedings, 2011
Series
IEEE Instrumentation and Measurement Technology Conference, ISSN 1091-5281
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-8514 (URN)10.1109/IMTC.2011.5944022 (DOI)000297171900158 ()2-s2.0-80051886176 (Scopus ID)978-1-4244-7933-7 (ISBN)978-1-4244-7935-1 (ISBN)
Conference
2011 IEEE International Instrumentation and Measurement Technology Conference I2MTC, Hangzhou, China, 10-12 May 2011
Available from: 2011-02-25 Created: 2011-02-25 Last updated: 2019-12-11Bibliographically approved
Nader, C., Van Moer, W., Barbé, K., Björsell, N. & Händel, P. (2011). Evolved Harmonic Sampling: a Tool to Reduce the Digital Bandwidth Requirement of RF Receivers. In: RFMTC11: . Paper presented at 2011 RF Measurement Technology Conference, October 4 to 5 2011, Gävle, Sweden. Gävle
Open this publication in new window or tab >>Evolved Harmonic Sampling: a Tool to Reduce the Digital Bandwidth Requirement of RF Receivers
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2011 (English)In: RFMTC11, Gävle, 2011Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Gävle: , 2011
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-11115 (URN)
Conference
2011 RF Measurement Technology Conference, October 4 to 5 2011, Gävle, Sweden
Available from: 2011-12-22 Created: 2011-12-22 Last updated: 2019-12-11Bibliographically approved
Nader, C., Van Moer, W., Barbé, K., Björsell, N. & Händel, P. (2011). Harmonic Sampling and Reconstruction of Wide-band Undersampled Waveforms: Breaking the Code. IEEE transactions on microwave theory and techniques, 59(11), 2961-2969
Open this publication in new window or tab >>Harmonic Sampling and Reconstruction of Wide-band Undersampled Waveforms: Breaking the Code
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2011 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 59, no 11, p. 2961-2969Article in journal (Refereed) Published
Place, publisher, year, edition, pages
IEEE Press, 2011
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-8517 (URN)10.1109/TMTT.2011.2161882 (DOI)000297093800020 ()2-s2.0-81455154490 (Scopus ID)
Available from: 2011-02-25 Created: 2011-02-25 Last updated: 2019-12-11Bibliographically approved
Fraile, F., Nader, C., Guerri, J. C. & Björsell, N. (2011). On the reuse of DVB-T transmitter infrastructure for DVB-T2. Paper presented at 2011 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, 8-10 June 2011, Nuremberg, Germany.
Open this publication in new window or tab >>On the reuse of DVB-T transmitter infrastructure for DVB-T2
2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The new DVB-T2 standard was specifically designed to allow the reuse of DVB-T infrastructure if required. This paper presents measurement results that verify the correct performance of a commercial DVB Power Amplifier with DVB-T2 waveforms. Furthermore, the paper includes configuration guidelines and performance evaluation of the Tone Reservation PAPR reduction algorithm included in the DVB-T2 standard. PAPR reduction is key technology when reusing DVB-T amplifiers for DVB-T2 transmissions without penalizing amplifier efficiency.

National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-9786 (URN)10.1109/BMSB.2011.5954964 (DOI)2-s2.0-80051980561 (Scopus ID)
Conference
2011 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, 8-10 June 2011, Nuremberg, Germany
Available from: 2011-07-22 Created: 2011-07-18 Last updated: 2019-12-11Bibliographically approved
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