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Khan, Zain Ahmed
Publications (7 of 7) Show all publications
Khan, Z. A. (2018). Characterization and Compensation of Hardware Impairments in Transmitters for Wireless Communications. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Characterization and Compensation of Hardware Impairments in Transmitters for Wireless Communications
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing demands for data rate, energy efficiency and reliability in wireless communications have resulted in the introduction of radio frequency (RF) multiple input multiple output (MIMO) transmitters. However, MIMO transmitters suffer from additional crosstalk impairments along with the power amplifier (PA) and I/Q imbalance distortions observed in single input single output (SISO) transmitters. Therefore, this thesis focuses on the characterization and compensation of these hardware impairments in RF SISO and MIMO transmitters.

PA distortions are often compensated using the Volterra series, but it suffers from high computational complexity. Therefore, a non-parametric method based on density estimation has been proposed in this thesis to estimate the PA transfer function, from which pruned Volterra models can be developed. The method is validated for a Doherty PA and achieves competitive error performance at a lower complexity than its competitors.

For MIMO transmitters, a characterization technique that uses multitone excitation signals has been proposed. Multitone signals yield non-overlapping tones at the outputs of the MIMO Volterra kernels. These kernel outputs are used to identify the dominant crosstalk impairments, from which block structure and base-band behavioral models are developed. The method is validated for 2x2 and 3x3 MIMO transmitters and it is shown that the derived models achieve a better complexity accuracy trade-off than the other pruned MIMO Volterra models considered in this thesis.

Finally, the thesis presents compensation models for joint static I/Q imbalance and MIMO PA distortions based on conjugate pair and real-valued basis functions. The models are augmented with sub-sample resolution to compensate for dynamic I/Q imbalance distortions. The proposed models are validated for a 2x2 RF MIMO transmitter and achieve a better complexity accuracy trade-off than the other state-of-the-art models considered in this thesis.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 65
Series
TRITA-EECS-AVL ; 2018:60
Keywords
Power amplifier, RF transmitters, SISO, MIMO, crosstalk, Volterra series, Volterra kernels, behavioral modeling, DPD, Ramanujan sums, multitone signals, I/Q Imbalance, non-linearity, memory polynomial, density estimation, hardware impairments
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-27935 (URN)978-91-7729-924-0 (ISBN)
Public defence
2018-10-18, Hörsal 12:108, Kungsbäcksvägen 47, Gävle, 13:15 (English)
Opponent
Supervisors
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2018-09-24Bibliographically approved
Khan, Z. A., Zenteno, E., Händel, P. & Isaksson, M. (2018). Extraction of the Third-Order 3x3 MIMO Volterra Kernel Outputs Using Multitone Signals. IEEE transactions on microwave theory and techniques, 66(11), 4985-4999
Open this publication in new window or tab >>Extraction of the Third-Order 3x3 MIMO Volterra Kernel Outputs Using Multitone Signals
2018 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, no 11, p. 4985-4999Article in journal (Refereed) Published
Abstract [en]

This paper uses multitone signals to simplify the analysis of 3×3 multiple-input multiple-output (MIMO) Volterra systems by isolating the third-order kernel outputs from each other. Multitone signals fed to an MIMO Volterra system yield a spectrum that is a permutation of the sums of the input signal tones. This a priori knowledge is used to design multitone signals such that the third-order kernel outputs are isolated in the frequency domain. The signals are designed by deriving the conditions for the offset and spacing of the input frequency grids. The proposed technique is then validated for the six possible configurations of a 3x3 RF MIMO transmitter impaired by crosstalk effects. The proposed multitone signal design is used to extract the third-order kernel outputs, and their relative contributions are analyzed to determine the dominant crosstalk effects for each configuration.

Place, publisher, year, edition, pages
IEEE, 2018
Keywords
Crosstalk; hardware impairments; multiple-input multiple-output (MIMO); multitone signals; Volterra kernels
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-27812 (URN)10.1109/TMTT.2018.2854186 (DOI)000449354500028 ()2-s2.0-85052719621 (Scopus ID)
Available from: 2018-09-01 Created: 2018-09-01 Last updated: 2019-11-29Bibliographically approved
Amin, S., Khan, Z. A., Isaksson, M., Händel, P. & Rönnow, D. (2016). Concurrent dual-band power amplifier model modification using dual two-tone test. In: 46th Europena Microwave Conference (EUMC) 2016: . Paper presented at 46th European Microwave Conference (EuMC), 4-6 October 2016, London, UK (pp. 186-189).
Open this publication in new window or tab >>Concurrent dual-band power amplifier model modification using dual two-tone test
Show others...
2016 (English)In: 46th Europena Microwave Conference (EUMC) 2016, 2016, p. 186-189Conference paper, Published paper (Refereed)
Abstract [en]

A dual two-tone technique for the characterization of memory effects in concurrent dual-band transmitters is revisited to modify a 2D-DPD model for the linearization of concurrent dual-band transmitters. By taking into account the individual nonlinear memory effects of the self- and cross-kernels, a new2D modified digital pre-distortion (2D-MDPD) model is proposed,which not only supersedes the linearization performance but also reduces the computational complexity compared to the 2DDPDmodel in terms of a number of floating point operations(FLOPs). Experimental results show an improvement of 1.7 dBin normalized mean square error (NMSE) and a 58% reduction in the number of FLOPs.

Series
European Microwave Conference, ISSN 2325-0305
Keywords
IEEE Keywords Computational modeling, Numerical models, Dual band, Two dimensional displays, Radio frequency, Computational complexity
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-22558 (URN)10.1109/EuMC.2016.7824309 (DOI)000393581100048 ()2-s2.0-85015185570 (Scopus ID)978-2-87487-043-9 (ISBN)978-1-5090-1514-6 (ISBN)
Conference
46th European Microwave Conference (EuMC), 4-6 October 2016, London, UK
Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2018-12-03Bibliographically approved
Zenteno, E., Khan, Z. A., Isaksson, M. & Händel, P. (2016). Finding Structural Information about RF Power Amplifiers using an Orthogonal Nonparametric Kernel Smoothing Estimator. IEEE Transactions on Vehicular Technology, 65(5), 2883-2889, Article ID 7109926.
Open this publication in new window or tab >>Finding Structural Information about RF Power Amplifiers using an Orthogonal Nonparametric Kernel Smoothing Estimator
2016 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, no 5, p. 2883-2889, article id 7109926Article in journal (Refereed) Published
Abstract [en]

A non-parametric technique for modeling the behavior of power amplifiers is presented. The proposed technique relies on the principles of density estimation using the kernel method and is suited for use in power amplifier modeling. The proposed methodology transforms the input domain into an orthogonal memory domain. In this domain, non-parametric static functions are discovered using the kernel estimator. These orthogonal, non-parametric functions can be fitted with any desired mathematical structure, thus facilitating its implementation. Furthermore, due to the orthogonality, the non-parametric functions can be analyzed and discarded individually, which simplifies pruning basis functions and provides a tradeoff between complexity and performance. The results show that the methodology can be employed to model power amplifiers, therein yielding error performance similar to state-of-the-art parametric models. Furthermore, a parameter-efficient model structure with 6 coefficients was derived for a Doherty power amplifier, therein significantly reducing the deployment’s computational complexity. Finally, the methodology can also be well exploited in digital linearization techniques.

Keywords
Power amplifier, non-parametric model, kernel, basis functions, power amplifier linearization, Digital pre distortion.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:hig:diva-19395 (URN)10.1109/TVT.2015.2434497 (DOI)000376094500004 ()2-s2.0-84970016798 (Scopus ID)
Available from: 2015-05-27 Created: 2015-05-27 Last updated: 2018-11-26Bibliographically approved
Zenteno, E., Khan, Z. A., Isaksson, M. & Händel, P. (2016). Using Intrinsic Integer Periodicity to Decompose the Volterra Structure in Multi-Channel RF Transmitters. IEEE Microwave and Wireless Components Letters, 26(4), 297-299
Open this publication in new window or tab >>Using Intrinsic Integer Periodicity to Decompose the Volterra Structure in Multi-Channel RF Transmitters
2016 (English)In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 26, no 4, p. 297-299Article in journal (Refereed) Published
Abstract [en]

An instrumentation, measurement and post-processing technique is presented to characterize transmitters by multiple input multiple output (MIMO) Volterra series. The MIMO Volterra series is decomposed as the sum of nonlinear single-variable self-kernels and a multi-variable cross-kernel. These kernels are identified by sample averages of the outputs using inputs of different sample periodicity. This technique is used to study the HW effects in a RF MIMO transmitter composed by input and output coupling filters (cross-talk) sandwiching a non-linear amplification stage. The proposed technique has shown to be useful in identifying the dominant effects in the transmitter structure and it can be used to design behavioral models and compensation techniques.

Keywords
Amplifiers, behavioral modeling, concurrent, digital predistortion, linearization, MIMO, MIMO Volterra series
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-21555 (URN)10.1109/LMWC.2016.2525019 (DOI)000374561900025 ()2-s2.0-84979470032 (Scopus ID)
Available from: 2016-06-10 Created: 2016-06-09 Last updated: 2018-11-26Bibliographically approved
Khan, Z. A., Zenteno, E., Händel, P. & Isaksson, M. (2015). Study of the Power Amplifier transfer function symmetry and its relation to dynamic effects. In: 2015 IEEE 16th Annual Wireless and Microwave Technology Conference (WAMICON): . Paper presented at 16th IEEE Annual Wireless and Microwave Technology Conference, WAMICON 2015, 13-15 April 2015, Cocoa Beach, United States (pp. 1-6). IEEE conference proceedings
Open this publication in new window or tab >>Study of the Power Amplifier transfer function symmetry and its relation to dynamic effects
2015 (English)In: 2015 IEEE 16th Annual Wireless and Microwave Technology Conference (WAMICON), IEEE conference proceedings, 2015, p. 1-6Conference paper, Published paper (Refereed)
Abstract [en]

Future wireless networks will employ unprecedentedly high number of transmitters along-with larger bandwidth signals. Therefore, complexity efficient Power Amplifier (PA) modelling methods with the ability to quantify memory effects are required. This paper presents a low complexity method to quantify memory effects by studying the symmetry in the PA transfer functions estimated with the density estimation method. It is shown that the symmetry helps in reducing the method complexity by more than two orders of magnitude. Further, it is verified that the symmetry can be used as a non-model based metric for quantifying memory effects in PAs. 

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Keywords
Complex networks, Crystal symmetry, Dynamics, Microwave devices, Probability density function, Transfer functions, Amplifier models, Density estimation, Density estimation methods, Efficient power, Future wireless networks, Method complexity, Modelling method, Orders of magnitude, Power amplifiers
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-20422 (URN)10.1109/WAMICON.2015.7120407 (DOI)000380567600059 ()2-s2.0-84942626353 (Scopus ID)978-1-4799-7521-1 (ISBN)
Conference
16th IEEE Annual Wireless and Microwave Technology Conference, WAMICON 2015, 13-15 April 2015, Cocoa Beach, United States
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2018-11-26Bibliographically approved
Khan, Z. A., Zenteno, E., Händel, P. & Isaksson, M.Identification of Third Order 3x3 MIMO Volterra Kernels using Multitone Excitation Signals.
Open this publication in new window or tab >>Identification of Third Order 3x3 MIMO Volterra Kernels using Multitone Excitation Signals
(English)Manuscript (preprint) (Other academic)
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-27934 (URN)
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2018-09-24Bibliographically approved
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