Low Complexity Equalization for Doubly Selective Channels Modeled by a Basis Expansion

Hrycak, Tomasz; Das, Saptarshi; Matz, Gerald; Feichtinger, Hans G.

doi:10.1109/tsp.2010.2063426

Cited by 62 publications

(50 citation statements)

References 32 publications

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“…It is important to underscore that since the bandwidth B band are not parallel to each other as in the narrowband case. A banded approximation of the channel matrix is crucial to many low-complexity equalizers, e.g., [5][6][7]18]. The equalizer considered in this article will also adopt this approximation to reduce the complexity.…”

Section: Interference Analysismentioning

confidence: 99%

“…In order to speed up the convergence of the iterative equalization, we then design a diagonal preconditioner to improve the condition of this banded matrix. It is noteworthy here that our preconditioner design is adapted from [17,18] to enhance its suitability for our MSML scenario. Finally, iterative equalization is proposed on the preconditioned channel matrix.…”

Section: Channel Equalization Schemementioning

confidence: 99%

“…To achieve a balance between performance and complexity, we restrict the preconditioner to be a diagonal matrix, whose diagonal entries can be designed by following the steps given in [17]. We notice that a circulant preconditioner in the time domain was introduced in [18], which is equivalent to a diagonal preconditioner in the frequency domain. This preconditioner is introduced based on a basis expansion model (BEM), which is often used to approximate the channel's time-variation for a narrowband system.…”

Section: Introductionmentioning

confidence: 99%

“…What is not considered in [17,18] is the resampling operation at the receiver, which is an indispensable and crucial step for wideband LTV channels. Different from the trivial resampling scheme for SSML channel models, an optimum resampling method is proposed in [14] for MSML channels, which aims at minimizing the average error of approximating the MSML channel by an SSML model.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Iterative equalization for OFDM systems over wideband Multi-Scale Multi-Lag channels

Tang

Remis

et al. 2012

J Wireless Com Network

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OFDM suffers from inter-carrier interference (ICI) when the channel is time varying. This article seeks to quantify the amount of interference resulting from wideband OFDM channels, which are assumed to follow the multi-scale multi-lag (MSML) model. The MSML channel model results in full channel matrices both in the frequency and time domains. However, banded approximations are possible, leading to a significant reduction in the equalization complexity. Measures for determining whether a time-domain or frequency-domain approach should be undertaken are provided based on the interference analysis, and we propose to use the conjugate gradient (CG) algorithm to equalize the channel iteratively. The suitability of a preconditioning technique, that often accompanies the CG method to accelerate the convergence, is also discussed. We show that in order for the diagonal preconditioner to function properly, optimal resampling is indispensable.

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Section: Interference Analysismentioning

confidence: 99%

Section: Channel Equalization Schemementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Iterative equalization for OFDM systems over wideband Multi-Scale Multi-Lag channels

Tang

Remis

et al. 2012

J Wireless Com Network

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“…At the same time, we desire that the design and implementation of the preconditioner should be simple enough such that the overall complexity stays low. A common practice is to restrict the preconditioner to be a diagonal matrix such as in [9], whose diagonal entries can be designed following the steps given in [10]. However, in the case where the major channel energy is located on the offdiagonals of the channel matrix, we can show that a diagonal preconditioner will render a negative effect on the channel matrix spectrum by clustering the eigenvalues around 0 instead of 1.…”

Section: Introductionmentioning

confidence: 99%

Equalization for multi-scale multi-lag OFDM channels

Tang

Remis

et al. 2011

2011 49th Annual Allerton Conference on Communication, Control, and Computing (Allerton)

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Abstract-We consider an orthogonal frequency-division multiplexing (OFDM) transmission scheme over wideband underwater acoustic channels, where the propagation paths can experience distinct Doppler effects (manifested in signal scales) and time of arrivals (manifested in lags). We capture such an effect in this paper with a multi-scale multi-lag (MSML) model, and show that the resulting frequency-domain MSML-OFDM channel is subject to inter-carrier interference (ICI), whose amount differs per subcarrier. The corresponding channel matrix can still be approximated as highly sparse, but lacks a specific structure that can optimally be exploited by those low-complexity equalizers proposed for narrowband channels. In this paper, we propose to use the conjugate gradient (CG) algorithm to equalize the channel iteratively. The suitability of the preconditioning technique, that often accompanies the CG to accelerate the convergence, is discussed for the MSML-OFDM channel. We show that in order for the preconditioner to function properly, optimal resampling is indispensible.

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