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Prasad, Sathyaveer
Publications (10 of 11) Show all publications
Alayón Glazunov, A., Prasad, S. & Händel, P. (2014). Experimental Characterization of the Propagation Channel along aVery Large Virtual Array in a Reverberation Chamber. Progress in Electromagnetics Research B, 59, 205-217
Open this publication in new window or tab >>Experimental Characterization of the Propagation Channel along aVery Large Virtual Array in a Reverberation Chamber
2014 (English)In: Progress in Electromagnetics Research B, ISSN 1937-6472, E-ISSN 1937-6472, Vol. 59, p. 205-217Article in journal (Refereed) Published
Abstract [en]

We show that the combined use of radio frequency absorbers and directive antennas can produce significant changes of the radio propagation channel properties along the positions of a virtual array inside a reverberation chamber. A multidimensional characterization of the channel was performed at 40 antenna positions with spacing of 0:233λ at 1 GHz. The average power, the Ricean K-factor, the coherence bandwidth, the r.m.s. delay spread, the mean delay, the beamforming power angle spectrum and array antenna correlation have been studied for different arrangements in the reverberation chamber. The analysis shows that the joint average over time and frequency channel behavior is, as expected, rather homogeneous along the very large array. However, individual realizations of the channel present a pronounced selective behavior in space, time and frequency with parameters varying along the positions of the virtual array suggesting that a heterogeneous behavior of the radio channels can be emulated in reverberation chambers. An important application of the presented study comprises testing of antenna array designs and algorithms in multipath environments. Further development may lead to Over The Air testing of Multiple Input Multiple Output antenna systems of various sizes, i.e., from small to very large arrays.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-18531 (URN)10.2528/PIERB14031203 (DOI)2-s2.0-84901462104 (Scopus ID)
Available from: 2014-12-12 Created: 2014-12-12 Last updated: 2018-03-13Bibliographically approved
Glazunov, A. A., Prasad, S., Händel, P., Bolin, T. & Prytz, K. (2014). Impact of Scattering Within a Multipath Simulator Antenna Array on the Ricean Fading Distribution Parameters in OTA Testing. IEEE Transactions on Antennas and Propagation, 62(6), 3257-3269
Open this publication in new window or tab >>Impact of Scattering Within a Multipath Simulator Antenna Array on the Ricean Fading Distribution Parameters in OTA Testing
Show others...
2014 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 62, no 6, p. 3257-3269Article in journal (Refereed) Published
Abstract [en]

In this paper, we investigate the unwanted scattering that exists within the multipath simulator (MPS) array antennas employed in over the air (OTA) testing of mobile terminals. The impact of scattering is evaluated in terms of the measurement uncertainty of the average received power and the Ricean K-factor. The maximum ratio combining diversity is investigated for a generic device under test comprising two half-wavelength dipole antennas. We provide closed-form expressions for the uncertainties of the average received power and the Ricean K-factor for a uniform circular array of MPS antennas and a 2-D uniformly distributed angle-of-arrival spectrum. We also derive the maximum number of MPS antennas and the minimum ring radius of the MPS system as a function of the separation between the most distant antenna elements if the device under test employs a uniform linear array. As a result, we provide design guidelines for MPS array in terms of the number antennas, the radius of the MPS array and the wavelength of the carrier frequency.

Keyword
Maximum ratio combining diversity, measurement accuracy, multipath simulator (MPS), Ricean K-factor, scattering
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-17650 (URN)10.1109/TAP.2014.2310191 (DOI)000337122100038 ()2-s2.0-84902000460 (Scopus ID)
Funder
EU, European Research Council, 228044
Available from: 2014-12-09 Created: 2014-10-08 Last updated: 2018-03-13Bibliographically approved
Prasad, S. (2013). Over-the-Air Performance Estimation of Wireless Device Antennas. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Over-the-Air Performance Estimation of Wireless Device Antennas
2013 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

This thesis work presents studies on the available measurement methods for estimating the over-the-air (OTA) performance of wireless device antennas. This thesis is divided into two parts. The first part is focused on studies of single-input single-output (SISO) OTA measurement methods and the second part is focused on studies of multiple-input multiple-output (MIMO) OTA measurement methods.

In the first part, the three methods for estimating the up-link radio performance of mobile phone antennas are evaluated, including the “EMSCAN Lab Express” planar near-field system, the “Telia Scattered Field Measurement method (TSFM),” and the “Bluetest” reverberation chamber. These methods are compared to the standard reference anechoic chamber methods.

Each method is experimentally evaluated by measuring the total radiated power from a number of commercially available mobile phones in addition to comparing the measurements to the results from a standard reference system. The comparison is performed statistically using simple regression analysis. For the reverberation chamber (RC), applying simple physical and statistical modeling extends the analysis. In particular, a maximum likelihood (ML) estimator for the Rician K−factor is derived, followed by both statistical and experimental evaluations.

Based on the results of the first part of this thesis, it can be concluded that the EMSCAN Lab Express planar near-field method overestimates the uplink performance of mobile phones, consequently introducing an error. The up-link performance of mobile phones estimated using the TSFM method agrees with the reference method but suffers from problems such as extensive measurement time and poor repeatability. The Bluetest RC method estimates the uplink performance of mobile phones well. However, the Rician K−factor computed from the ML estimator is found to be greater than zero, indicating an inadequacy in the propagation environment inside the RC.

In the second part, the anechoic chamber-multipath simulator (MPS) and the RC-very large MIMO (VLM) OTA testing methods are studied.

In the MPS method, the impact of scattering within the MPS array antennas on the Rician fading statistics is addressed by performing simulations and measurements based on the proposed MPS scattering model and the derived far-field criteria. The results of the investigation suggest that to minimize the impact of scattering, a large MPS system must be designed, although it will result in higher costs. In turn, the costs can be lowered by miniaturizing the MPS system, which can be achieved by following the derived far-field (Fraunhofer distance) criteria. Thus, miniaturization will also allow the measurement uncertainties to be restricted at an acceptable level.

In the VLM OTA testing method, the study is based on very large virtual uniform linear array measurements and focuses on the multidimensional characterization of the channel transfer function and the channel impulse response of the reverberation chamber. The results of this study suggest that the reverberation chamber can be used to emulate the more realistic channels for testing the VLM antenna systems.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. p. xiv, 186
Series
TRITA-EE, ISSN 1653-5146 ; 2013:004
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-18278 (URN)978-91-7501-638-2 (ISBN)
Public defence
2013-03-08, Hörsal 99131, Högskolan i Gävle, Kungsbäcksvägen 47, 13:15 (English)
Opponent
Supervisors
Available from: 2014-12-09 Created: 2014-12-05 Last updated: 2018-03-13Bibliographically approved
Ghahfarokhi, S. S., Prasad, S. & Tayari, D. (2011). Impact of Moisture Content on RFID Antenna Performance for Wood-Log Monitoring. In: RFMTC11: . Paper presented at 2011 RF Measurement Technology Conference, October 4 to 5 2011, Gävle, Sweden. Gävle, Sweden
Open this publication in new window or tab >>Impact of Moisture Content on RFID Antenna Performance for Wood-Log Monitoring
2011 (English)In: RFMTC11, Gävle, Sweden, 2011Conference paper, Published paper (Other academic)
Abstract [en]

In recent years, the use of RFID technology has gained popularity in the timber industry for wood-log monitoring. Harvested wood-logs are stored for different time periods before being processed. As a result, the moisture content in the stored wood-logs varies compared to the freshly-cut wood and it must also be noted that the moisture content of freshly cut wood differs from one log to another. Apart from storage time period of wood-logs, the environmental factors such as temperature, rain, snow and sun also contributes to the variation in the moisture content of the wood-logs. This variation of the moisture content changes the dielectric constant of the wood and hence, influences the characteristics of the RFID antenna. In this paper the impact of variations in moisture content in wood and its effect on the performance of the RFID antenna are studied.

Place, publisher, year, edition, pages
Gävle, Sweden: , 2011
Keyword
RFID antenna, RFID tag, wood-log, moisture, dielectric constant
National Category
Telecommunications Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-9999 (URN)
Conference
2011 RF Measurement Technology Conference, October 4 to 5 2011, Gävle, Sweden
Available from: 2011-09-09 Created: 2011-09-02 Last updated: 2018-03-13Bibliographically approved
Prasad, S. (2011). Studies of Three Different Methods to Estimate the Up-link Performance of Mobile Phone Antennas. (Licentiate dissertation). Stockholm: Royal Institute of Technology (KTH)
Open this publication in new window or tab >>Studies of Three Different Methods to Estimate the Up-link Performance of Mobile Phone Antennas
2011 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

Antennas play an important role in determining the overall radio performance for wireless communications. If all other radio components perform according to their specifications, the performance of a mobile phone can be entirely determined by measuring the efficiency of its antenna. Poor performance of the mobile phone may result in reduced coverage, lower capacity and dissatisfied users. Hence, the ability to accurately and efficiently estimate the radio performance of the mobile phone antenna is of great importance to the telecommunications industry.

The mobile phone was originally a simple device that only transmitted voice, but it has evolved into a complicated terminal for high data-rate services. This evolution poses many new challenges to mobile phone antenna manufacturers. Antennas must be tested during design and production phases to optimize the in-network radio performance. Standardization bodies, such as the Cellular Telecommunications and Internet Association (CTIA) and the Third Generation Partnership Project (3GPP), have specified procedures for comprehensive testing of the up-link and down-link radio performance of the mobile phone, characterized by the total radiated power (TRP) and total isotropic sensitivity (TIS), respectively.

In this thesis, three methods for estimating the up-link radio performance of mobile phone antennas are evaluated: the "EMSCAN Lab Express" planar near field system; the "Telia Scattered Field Measurement method"; and the "Bluetest" reverberation chamber. These methods are compared to the reference CTIA- and 3GPP-approved anechoic chamber methods. Each method is experimentally evaluated by measuring the TRP from a number of commercially available mobile phones and comparing the measurements to the results from a standard reference system. The comparison is performed statistically using simple regression analysis. For the reverberation chamber, the analysis is extended by using simple physical and statistical modeling. In particular, a maximum likelihood (ML) estimator for the Rician K factor is derived, statistically and experimentally evaluated.

Based on the results of this thesis, it can be concluded that the EMSCAN Lab Express planar near field method overestimates the up-link performance of mobile phones, thus, introducing an error. The up-link performance of mobile phones estimated by the Telia scattered field measurement method agrees with the reference method, but suffers from problems such as extensive measurement time and poor repeatability. The Bluetest reverberation chamber method estimates the uplink performance of mobile phones well. However, the computed Rician K factor from the ML estimator is found to be greater than zero, indicating an inadequacy in the propagation environment inside the reverberation chamber. 

Place, publisher, year, edition, pages
Stockholm: Royal Institute of Technology (KTH), 2011. p. xii, 129
Series
Trita-EE, ISSN 1653-5146 ; 2011:015
Keyword
Antenna measurements, mobile phones, total radiated power, reverberation chamber, anechoic chamber, Telia Scattered Field Method, Maximum likelihood Estimator
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-10000 (URN)978-91-7415-781-9 (ISBN)
Opponent
Supervisors
Available from: 2011-09-09 Created: 2011-09-02 Last updated: 2018-03-13Bibliographically approved
Prasad, S. & Beckman, C. (2010). Comparison of Four Different Methods to Estimate the Radiated Power from Mobile Phones. In: 2010 Loughborough Antennas and Propagation Conference, LAPC 2010: . Paper presented at 6th Loughborough Antennas and Propagation Conference, LAPC 2010, 8-9 November, 2010, Loughborough United Kingdom (pp. 425-428). , Article ID 5666216.
Open this publication in new window or tab >>Comparison of Four Different Methods to Estimate the Radiated Power from Mobile Phones
2010 (English)In: 2010 Loughborough Antennas and Propagation Conference, LAPC 2010, 2010, p. 425-428, article id 5666216Conference paper, Published paper (Other academic)
Abstract [en]

In this paper, the radiated power is estimated for various commercially available mobile phones using the Telia Scattered Field Measurement method (TSFM), In-Network performance estimation and the EMSCAN near field scanner: "Lab-Express". The results are then compared with the radiated power measured using the Satimo Star Gate 64/24 system. Our measurement results suggest that the radiated power measured in the TSFM method correlates to a great extent both with the Star Gate System and the In-network method suggesting that the TSFM method can be used an alternative tool to in-network measurements and also can be used for standard reference measurements provided accuracy and repeatability are accounted according to the standards. However, the results from the Star Gate system were weakly correlated to the results from the Lab-Express suggesting that Lab-Express cannot replace Star Gate System for standard reference measurements but can only serve as a good tool for testing antennas during design and development phases.

Keyword
Radiated power, mobile phones, In-network, measurements
National Category
Signal Processing Telecommunications
Identifiers
urn:nbn:se:hig:diva-7459 (URN)10.1109/LAPC.2010.5666216 (DOI)2-s2.0-78651442158 (Scopus ID)978-142447305-2 (ISBN)
Conference
6th Loughborough Antennas and Propagation Conference, LAPC 2010, 8-9 November, 2010, Loughborough United Kingdom
Available from: 2010-09-03 Created: 2010-09-03 Last updated: 2018-03-13Bibliographically approved
Prasad, S., Halim, H. & Beckman, C. (2009). Evaluation of a Near Field Scanner for TRP and Radiation Pattern Measurements of GSM Mobile Phones. In: 3RD EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION: . Paper presented at 3rd European Conference on Antennas and Propagation, EUCAP2009, Berlin, Germany, 23-27 March 2009 (pp. 2122-2126). IEEE conference proceedings
Open this publication in new window or tab >>Evaluation of a Near Field Scanner for TRP and Radiation Pattern Measurements of GSM Mobile Phones
2009 (English)In: 3RD EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, IEEE conference proceedings, 2009, p. 2122-2126Conference paper, Published paper (Other academic)
Abstract [en]

In this paper a new tool for estimation of the radio performance of terminal antennas in terms of Total Radiated Power, TRP is tested and evaluated. The tool is known as Lab Express and is developed by the Canadian company EMSCAN.  The results from measurements performed with the Lab Express are compared with of the radiation patterns and total radiated power (TRP) estimates, measured with a CTIA approved Satimo SG24 chamber.

The TRP and radiation pattern measurements are performed on 10 commercially available mobile phones at GSM 900 and GSM 1800 frequency bands. The dependency of the measured TRP on the positioning of the mobile phone on EMSCAN is also tested. Our results indicate that the TRP measured with Lab Express is well correlated with the results obtained from the Satimo SG24 chamber even though the Lab Express equipment seem to over estimate the TRP with on average about 4dB at 900MHz and about 1.3dB at 1800MHz.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2009
Keyword
Lab Express, Antenna Measurements, Mobile Terminal Antenna, Total Radiated Power
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-3826 (URN)000276522101048 ()978-1-4244-4753-4 (ISBN)
Conference
3rd European Conference on Antennas and Propagation, EUCAP2009, Berlin, Germany, 23-27 March 2009
Available from: 2009-02-28 Created: 2009-02-28 Last updated: 2018-03-13Bibliographically approved
Händel, P., Prasad, S. & Beckman, C. (2009). Maximum likelihood estimation of reverberation chamber direct-to-scattered ratio [Letter to the editor]. Electronics Letters, 45(25), 1285-1286
Open this publication in new window or tab >>Maximum likelihood estimation of reverberation chamber direct-to-scattered ratio
2009 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, no 25, p. 1285-1286Article in journal, Letter (Refereed) Published
Abstract [en]

The exact maximum likelihood estimator of the direct-to-scattered ratio of the Rician channel in a reverberation chamber is derived and its performance analysed. It is shown that the estimator obeys a non-central F-distribution, the mean value and variance of which are derived. For well stirred chambers, it is shown that the systematic error in the estimated ratio may be significant.

Keyword
Reverberation chamber, Maximum Likelihood Estimator, Direct-to-Scattered ratio
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-6018 (URN)10.1049/el.2009.2489 (DOI)000273043100009 ()2-s2.0-72249095057 (Scopus ID)
Available from: 2009-12-17 Created: 2009-12-17 Last updated: 2018-03-13Bibliographically approved
Prasad, S., Medawar, S., Händel, P. & Beckman, C. (2008). Estimation of the Rician K-factor in Reverberation Chambers for Improved Repeatability in Terminal Antenna Measurements. In: 30th Annual Symposium of the Antenna Measurement Techniques Association (AMTA) (pp. 6). Boston, Mass.: AMTA-2008
Open this publication in new window or tab >>Estimation of the Rician K-factor in Reverberation Chambers for Improved Repeatability in Terminal Antenna Measurements
2008 (English)In: 30th Annual Symposium of the Antenna Measurement Techniques Association (AMTA), Boston, Mass.: AMTA-2008 , 2008, p. 6-Conference paper, Published paper (Other academic)
Abstract [en]

The in-network performance of the mobile phone depends highly on the terminal antennas. Their performance may reduce the coverage and the capacity of the whole network. Hence, an antenna measurement method that accurately emulates the in-network radio environment is much desired.

The reverberation, or mode-stirred, chamber is a cavity resonator with a high Q factor used for testing the performance of terminals and terminal antennas in a controlled field environment. In order to create a homogeneous field inside the chamber, emulating an isotropic multipath environment, mode stirrers are used.

The Rician K-factor is a statistical parameter that describes the field distribution in the chamber and is defined as the ratio of the unstirred to stirred field components in the chamber. This K-factor varies from zero to infinity. In order to be able to accurately repeat a measurement performed in a reverberation chamber it is, hence, of greatest importance to accurately determine the Rician K-factor from said measurements.

In this paper, a statistical model for the electromagnetic fields in reverberation chamber is reviewed for a Line of Sight (LOS) environment. An Estimator of the Rician K-factor is derived and its accuracy is verified.

Place, publisher, year, edition, pages
Boston, Mass.: AMTA-2008, 2008
Keyword
Rician K factor
Identifiers
urn:nbn:se:hig:diva-3439 (URN)
Available from: 2009-01-20 Created: 2008-12-29 Last updated: 2018-03-13Bibliographically approved
Prasad, S., Ramachandran, P., Glazunov, A. A. & Beckman, C. (2007). EVALUATION OF THE TELIA SCATTERED FIELD MEASUREMENT METHOD FOR ESTIMATION OF IN-NETWORK PERFORMANCE OF MOBILE TERMINAL ANTENNAS. St.Louis,USA: AMTA 2007
Open this publication in new window or tab >>EVALUATION OF THE TELIA SCATTERED FIELD MEASUREMENT METHOD FOR ESTIMATION OF IN-NETWORK PERFORMANCE OF MOBILE TERMINAL ANTENNAS
2007 (English)Conference paper, Published paper (Other academic)
Abstract [en]

In this paper we present and evaluate a method for estimation of in-network performance of mobile terminal antennas developed by the Swedish telecom operator Telia.

The Telia Scattered Field Measurement (TSFM) Method is intended to give a better estimate of the performance of the mobile terminal antenna as in an in-network fading scenario. The parameter measured from the TSFM method is referred to as the Scattered Field Measurement Gain, SFMG, i.e. the Mean Effective Gain, MEG, measured relative to a half wave dipole antenna. MEG includes the radiation pattern of the mobile terminal antenna as well as an estimate of polarization and directional losses that occur due to the propagation environment.

In this study it is found that the TSFM method provides a good measure of the in-network performance of the mobile terminal antenna. Furthermore, it is shown that the SFMG measured with this method is found to be well correlated with the Total Radiated Power Gain, TRPG, or radiation efficiency. This suggests that the Total Radiated Power, TRP, may be a good measure of the in-network performance of mobile terminal antennas if measured with proper adjustment to the antenna and propagation channel mismatch.

Place, publisher, year, edition, pages
St.Louis,USA: AMTA 2007, 2007
Keyword
Antenna Measurements, Mean Effective Gain, Mobile Terminal Antenna, TSFM method, Total Radiated Power.
National Category
Telecommunications
Identifiers
urn:nbn:se:hig:diva-5492 (URN)
Available from: 2009-11-03 Created: 2009-09-23 Last updated: 2018-03-13Bibliographically approved
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