Browsing by Author "Isaksson, Magnus"

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    Digital Predistortion for Joint Mitigation of I/Q Imbalance and MIMO Power Amplifier Distortion
    (Institute of Electrical and Electronics Engineers Inc., 2017) Ahmed Khan, Zain; Zenteno Bolaños, Efrain; Händel, Peter; Isaksson, Magnus
    This paper analyzes the joint effects of in-phase and quadrature (I/Q) imbalance and power amplifier (PA) distortion for RF multiple input multiple output (MIMO) transmitters in the presence of crosstalk. This paper proposes candidate models for the digital predistortion of static I/Q imbalanced sources exciting a dynamic MIMO Volterra system. The proposed models are enhanced using a novel technique based on subsample resolution to account for dynamic I/Q imbalance distortions. Finally, the computational complexity of the proposed models is analyzed for implementation suitability in digital platforms. It is shown that the error spectrum for the proposed models in subsample resolution reaches the noise floor of the measurements. The proposed models achieve a normalized mean squared error of-50 dB and an adjacent channel power ratio of-57 dB for signal bandwidths upto 65 MHz and crosstalk levels ranging to-10 dB. These results demonstrate the effectiveness of the proposed techniques in the joint mitigation of I/Q imbalance and PA distortion with crosstalk for a typical 2 × 2 MIMO telecommunication setup. © 2016 IEEE.
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    Extraction of the Third-Order 3 ×3 MIMO Volterra Kernel Outputs Using Multitone Signals
    (Institute of Electrical and Electronics Engineers Inc., 2018) Zain Ahmed, Khan; Zenteno Bolaños, Efrain; Händel, Peter; Isaksson, Magnus
    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 3 × 3 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. © 1963-2012 IEEE.
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    Multitene design for third order MIMO volterra kernels
    (Institute of Electrical and Electronics Engineers Inc., 2017) Zain Ahmed, Khan; Zenteno Bolaños, Efrain; Händel, Peter; Isaksson, Magnus
    This paper proposes a technique for designing multitone signals that can separate the third order multiple input multiple output (MIMO) Volterra kernels. Multitone signals fed to a 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 output from the MIMO Volterra kernels does not overlap in the frequency domain, hence making it possible to separate these kernels from the output of the MIMO Volterra system. The proposed technique is applied to a 2×2 RF MIMO transmitter to determine its dominant hardware impairments. For input crosstalk, the proposed method reveals the dominant self and cross kernels whereas for output crosstalk, the proposed method reveals that only the self kernels are dominant. © 2017 IEEE.
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    Pilot tone aided measurements to extend the bandwidth of radio frequency applications
    (Elsevier B.V., 2016) Zenteno Bolaños, Efrain; Isaksson, Magnus; Händel, Peter
    A technique to extend the effective measurement bandwidth of a non-coherent vector receiver is presented. This bandwidth extension technique relies on the use of a pilot signal (known a priori), which is added on the signal of interest and is measured in a single receiver. Compared to other bandwidth extension techniques referred as stitching techniques, the proposed approach avoids error propagation in the measurement bandwidth and simultaneously enables the measurement of signals that do not contain energy in certain spectral bands. The pilot signal is created in digital stages, which tackles to large extent the requirement of the a priori knowledge of this signal. Further, the pilot signal is designed to minimize estimation errors of the proposed technique, providing enhanced performance. It is analytically shown that the error incurred by the proposed method is always lower than the error from the measurement noise. Measurement results show the method functionality with an error in the range of -50 dB of the signal measured. Finally, the usefulness of the proposed technique is illustrated by measuring the input and output of an amplifier with dynamic range in excess of 80 dB over 290 MHz using an 18 MHz bandwidth receiver. This measurement could not have been performed by existing stitching techniques. © 2016 The Author(s). Published by Elsevier Ltd.
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    Using Intrinsic Integer Periodicity to Decompose the Volterra Structure in Multi-Channel RF Transmitter
    (Institute of Electrical and Electronics Engineers Inc., 2016) Zenteno Bolaños, Efrain; Zain Ahmed, Khan; Isaksson, Magnus; Händel, Peter
    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. © 2015 IEEE.