A Low-Complexity KL Expansion-Based Channel Estimator for OFDM Systems
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A Low-Complexity KL Expansion-Based Channel Estimator for OFDM Systems Habib S¸enol Department of Computer Engineering, Kadir Has University, Cibali 34230, Istanbul, Turkey Email: [email protected]
Hakan A. C¸ırpan Department of Electrical-Electronics Engineering, Istanbul University, Avcilar 34850, Istanbul, Turkey Email: [email protected]
Erdal Panayırcı Department of Electronics Enginering, IS¸ik University, Maslak 80670, Istanbul, Turkey Email: [email protected] Received 23 April 2004; Revised 18 October 2004 This paper first proposes a computationally efficient, pilot-aided linear minimum mean square error (MMSE) batch channel estimation algorithm for OFDM systems in unknown wireless fading channels. The proposed approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Moreover, optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the estimation algorithm. The performance of the proposed approach is studied through analytical and experimental results. We then consider the stochastic Cram´er-Rao bound and derive the closedform expression for the random KL coefficients and consequently exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also analyze the effect of a modelling mismatch on the estimator performance. To further reduce the complexity, we extend the batch linear MMSE to the sequential linear MMSE estimator. With the fast convergence property and the simple structure, the sequential linear MMSE estimator provides an attractive alternative to the implementation of channel estimator. Keywords and phrases: channel estimation, OFDM systems, MMSE estimation.
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INTRODUCTION
With unprecedented demands on bandwidth due to the explosive growth of broadband wireless services usage, there is an acute need for a high-rate and bandwidth-efficient digital transmission. In response to this need, the research community has been extensively investigating efficient schemes that make efficient utilization of the limited bandwidth and cope with the adverse access environments [1]. These access environments may create different channel impairments and dictate unique sets of advanced signal processing algorithms to combat specific impairments. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Multicarrier (MC) transmission scheme, especially orthogonal frequency-division multiplexing (OFDM), has recently attracted considerable attention since it has been shown to be an effective technique to combat delay spread or frequency-selective fading of wireless or wireline cha
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