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Physical layer considerations for wideband cognitive radio

Published in:
MILCOM 2010, IEEE Military Communications Conference , 31 October-3 November 2010, pp. 2113-2118.

Summary

Next generation cognitive radios will benefit from the capability of transmitting and receiving communications waveforms across many disjoint frequency channels spanning hundreds of megahertz of bandwidth. The information theoretic advantages of multi-channel operation for cognitive radio (CR), however, come at the expense of stringent linearity requirements on the analog transmit and receive hardware. This paper presents the quantitative advantages of multi-channel operation for next generation CR, and the advanced digital compensation algorithms to mitigate transmit and receive nonlinearities that enable broadband multi-channel operation. Laboratory measurements of the improvement in the performance of a multi-channel CR communications system operating below 2 GHz in over 500 MHz of instantaneous bandwidth are presented.
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Summary

Next generation cognitive radios will benefit from the capability of transmitting and receiving communications waveforms across many disjoint frequency channels spanning hundreds of megahertz of bandwidth. The information theoretic advantages of multi-channel operation for cognitive radio (CR), however, come at the expense of stringent linearity requirements on the analog transmit...

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A log-frequency approach to the identification of the Wiener-Hammerstein model

Published in:
IEEE Sig. Proc. Lett., Vol. 16, No. 10, October 2009, pp. 889-892.

Summary

In this paper we present a simple closed-form solution to the Wiener-Hammerstein (W-H) identification problem. The identification process occurs in the log-frequency domain where magnitudes and phases are separable. We show that the theoretically optimal W-H identification is unique up to an amplitude, phase and delay ambiguity, and that the nonlinearity enables the separate identification of the individual linear time invariant (LTI) components in a W-H architecture.
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Summary

In this paper we present a simple closed-form solution to the Wiener-Hammerstein (W-H) identification problem. The identification process occurs in the log-frequency domain where magnitudes and phases are separable. We show that the theoretically optimal W-H identification is unique up to an amplitude, phase and delay ambiguity, and that the...

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Polyphase nonlinear equalization of time-interleaved analog-to-digital converters

Published in:
IEEE J. Sel. Top. Sig. Process., Vol. 3, No. 3, June 2009, pp. 362-373.

Summary

As the demand for higher data rates increases, commercial analog-to-digital converters (ADCs) are more commonly being implemented with multiple on-chip converters whose outputs are time-interleaved. The distortion generated by time-interleaved ADCs is now not only a function of the nonlinear behavior of the constituent circuitry, but also mismatches associated with interleaving multiple output streams. To mitigate distortion generated by time-interleaved ADCs, we have developed a polyphase NonLinear EQualizer (pNLEQ) which is capable of simultaneously mitigating distortion generated by both the on-chip circuitry and mismatches due to time interleaving. In this paper, we describe the pNLEQ architecture and present measurements of its performance.
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Summary

As the demand for higher data rates increases, commercial analog-to-digital converters (ADCs) are more commonly being implemented with multiple on-chip converters whose outputs are time-interleaved. The distortion generated by time-interleaved ADCs is now not only a function of the nonlinear behavior of the constituent circuitry, but also mismatches associated with...

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Extending the dynamic range of RF receivers using nonlinear equalization

Summary

Systems currently being developed to operate across wide bandwidths with high sensitivity requirements are limited by the inherent dynamic range of a receiver's analog and mixed-signal components. To increase a receiver's overall linearity, we have developed a digital NonLinear EQualization (NLEQ) processor which is capable of extending a receiver's dynamic range from one to three orders of magnitude. In this paper we describe the NLEQ architecture and present measurements of its performance.
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Summary

Systems currently being developed to operate across wide bandwidths with high sensitivity requirements are limited by the inherent dynamic range of a receiver's analog and mixed-signal components. To increase a receiver's overall linearity, we have developed a digital NonLinear EQualization (NLEQ) processor which is capable of extending a receiver's dynamic...

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A polyphase nonlinear equalization architecture and semi-blind identification method

Published in:
42th Asilomar Conf. on Signals, Systems, and Computers, 27 October 2008, pp. 593-597.

Summary

In this paper, we present an architecture and semiblind identification method for a polyphase nonlinear equalizer (pNLEQ). Such an equalizer is useful for extending the dynamic range of time-interleaved analog-to-digital converters (ADCs). Our proposed architecture is a polyphase extension to other architectures that partition the Volterra kernel into small nonlinear filters with relatively low computational complexity. Our semi-blind identification technique addresses important practical concerns in the equalizer identification process. We describe our architecture and demonstrate its performance with measured results when applied to a National Semiconductor ADC081000.
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Summary

In this paper, we present an architecture and semiblind identification method for a polyphase nonlinear equalizer (pNLEQ). Such an equalizer is useful for extending the dynamic range of time-interleaved analog-to-digital converters (ADCs). Our proposed architecture is a polyphase extension to other architectures that partition the Volterra kernel into small nonlinear...

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The cube coefficient subspace architecture for nonlinear digital predistortion

Published in:
42th Asilomar Conf. on Signals, Systems, and Computers, 27 October 2008, pp. 1857-1861.

Summary

In this paper, we present the cube coefficient subspace (CCS) architecture for linearizing power amplifiers (PAs), which divides the overparametrized Volterra kernel into small, computationally efficient subkernels spanning only the portions of the full multidimensional coefficient space with the greatest impact on linearization. Using measured results from a Q-Band solid state PA, we demonstrate that the CCS predistorter architecture achieves better linearization performance than state-of-the-art memory polynomials and generalized memory polynomials.
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Summary

In this paper, we present the cube coefficient subspace (CCS) architecture for linearizing power amplifiers (PAs), which divides the overparametrized Volterra kernel into small, computationally efficient subkernels spanning only the portions of the full multidimensional coefficient space with the greatest impact on linearization. Using measured results from a Q-Band solid...

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A new approach to achieving high-performance power amplifier linearization

Published in:
IEEE Radar Conf., 17-20 April 2007. doi: 10.1109/RADAR.2007.374329

Summary

Digital baseband predistortion (DBP) is not particularly well suited to linearizing wideband power amplifiers (PAs); this is due to the exorbitant price paid in computational complexity. One of the underlying reasons for the computational complexity of DBP is the inherent inefficiency of using a sufficiently deep memory and a high enough polynomial order to span the multidimensional signal space needed to mitigate PA-induced nonlinear distortion. Therefore we have developed a new mathematical method to efficiently search for and localize those regions in the multidimensional signal space that enable us to invert PA nonlinearities with a significant reduction in computational complexity. Using a wideband code division multiple access (CDMA) signal we demonstrate and compare the PA linearization performance and computational complexity of our algorithm to that of conventional DBP techniques using measured results.
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Summary

Digital baseband predistortion (DBP) is not particularly well suited to linearizing wideband power amplifiers (PAs); this is due to the exorbitant price paid in computational complexity. One of the underlying reasons for the computational complexity of DBP is the inherent inefficiency of using a sufficiently deep memory and a high...

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