TY - JOUR
T1 - Subspace-Based Estimation of Rapidly Varying Mobile Channels for OFDM Systems
AU - Senol, Habib
AU - Tepedelenlioglu, Cihan
N1 - Funding Information:
Manuscript received April 29, 2020; revised September 11, 2020 and December 4, 2020; accepted December 13, 2020. Date of publication December 17, 2020; date of current version January 11, 2021. The associate editor coordinating the review of this manuscript and approving it for publication was Dr. Sangarapillai Lambotharan. The work of Habib S¸enol was supported by The Scientific and Technological Research Council of Turkey (TÜB˙TAK) between September 2018 and June 2019. (Corresponding author: Habib S¸enol.) Habib S¸enol is with the Department of Computer Engineering, Kadir Has University, 34 083 Istanbul, Turkey (e-mail: hsenol@khas.edu.tr).
Publisher Copyright:
© 1991-2012 IEEE.
PY - 2021
Y1 - 2021
N2 - It is well-known that time-varying channels can provide time diversity and improve error rate performance compared to time-invariant fading channels. However, exploiting time diversity requires very accurate channel estimates at the receiver. In order to reduce the number of unknown channel coefficients while estimating the time-varying channel, basis expansion models can be used along with long transmission frames that contain multiple orthogonal frequency division multiplexing (OFDM) symbols that experience the channel variation. The design of these OFDM frames need to judiciously incorporate training and data insertions in the transmitted signal while maintaining orthogonality. In this work, we propose an inter channel interference (ICI)-free training model depending on pilot symbols only and provide a corresponding time-varying channel estimation method. This scheme relies on an algorithm to determine the number of OFDM symbols per frame and the number of basis functions per path with minimal information about the Doppler bandwidth. As a performance benchmark, Bayesian Cramér Rao lower bound (CRLB) and the corresponding MSE bound are derived analytically for the proposed training model. Theoretical MSE expressions of the proposed estimation scheme are also derived as well as the MSE expressions in the presence of Doppler frequency mismatch. Simulations exhibit substantial MSE improvement and the corresponding Symbol Error Rate (SER) performances of the low complexity estimation scheme. They also corroborate that, unlike the common results in the literature, an OFDM system can perform better as the Doppler frequency increases with judicious design of training and channel estimation schemes.
AB - It is well-known that time-varying channels can provide time diversity and improve error rate performance compared to time-invariant fading channels. However, exploiting time diversity requires very accurate channel estimates at the receiver. In order to reduce the number of unknown channel coefficients while estimating the time-varying channel, basis expansion models can be used along with long transmission frames that contain multiple orthogonal frequency division multiplexing (OFDM) symbols that experience the channel variation. The design of these OFDM frames need to judiciously incorporate training and data insertions in the transmitted signal while maintaining orthogonality. In this work, we propose an inter channel interference (ICI)-free training model depending on pilot symbols only and provide a corresponding time-varying channel estimation method. This scheme relies on an algorithm to determine the number of OFDM symbols per frame and the number of basis functions per path with minimal information about the Doppler bandwidth. As a performance benchmark, Bayesian Cramér Rao lower bound (CRLB) and the corresponding MSE bound are derived analytically for the proposed training model. Theoretical MSE expressions of the proposed estimation scheme are also derived as well as the MSE expressions in the presence of Doppler frequency mismatch. Simulations exhibit substantial MSE improvement and the corresponding Symbol Error Rate (SER) performances of the low complexity estimation scheme. They also corroborate that, unlike the common results in the literature, an OFDM system can perform better as the Doppler frequency increases with judicious design of training and channel estimation schemes.
KW - Basis expansion model (BEM)
KW - channel estimation
KW - null space
KW - orthogonal frequency-division multiplexing (OFDM)
KW - rapidly varying multipath channel
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U2 - 10.1109/TSP.2020.3045562
DO - 10.1109/TSP.2020.3045562
M3 - Article
AN - SCOPUS:85098774652
SN - 1053-587X
VL - 69
SP - 385
EP - 400
JO - IEEE Transactions on Signal Processing
JF - IEEE Transactions on Signal Processing
M1 - 9296822
ER -