Abstract
A low-complexity pilot pattern and a frequency-domain channel estimation method for Inter-Carrier Interference (ICI) mitigation is proposed for Orthogonal Frequency Division Multiple Access (OFDM) systems. The proposed method exploits the band structure of the coupling matrix to perform an ICI-free channel estimation in the frequency domain. This ICI-free estimation relies on some conditions imposed over the pilot pattern that simplify the complexity of channel estimation significantly, since its complexity is the same as classical least squares (LS) channel estimation used in low mobility scenarios. Then, the ICI is removed by using a modified version of Minimum Mean Square Error (MMSE) equalization, which reduces the computational complexity considerably. This modified MMSE equalization relies on the sparse and banded structure of the coupling matrix and on a low complexity variant of the Cholesky decomposition, which is named LDLH factorization. It is shown that the proposed method greatly improves the Bit Error Rate (BER) in the high Signal-to-Noise Ratio (SNR) regime.
Highlights
Orthogonal frequency division multiplexing (OFDM) has been widely applied to different areas such as digital video broadcasting, power-line communications, underwater communications, wireless local area networks and cellular communications, among others
It can be observed that the proposed method with spline interpolation in the time domain achieves the best performance in the high Signal-to-Noise Ratio (SNR) regime
Zero Order Hold (ZOH) interpolation provides the worst Bit Error Rate (BER) results whereas spline method achieves the lowest BER. This is because there is inter-carrier interference (ICI) in the channel estimation, the channel is outdated between OFDM symbols without pilots, and ICI is not mitigated with the equalization
Summary
Orthogonal frequency division multiplexing (OFDM) has been widely applied to different areas such as digital video broadcasting, power-line communications, underwater communications, wireless local area networks and cellular communications, among others. Sophisticated channel estimation schemes can increase the receiver complexity, and the pilot pattern must be carefully devised to avoid reducing the spectral efficiency All these issues motivated us to investigate channel estimation and linear equalization for ICI mitigation with reduced complexity. In this paper we propose a low-complexity pilot pattern and a novel frequency domain coupling matrix estimation for ICI mitigation in OFDM systems. Where Hd(mf )(d, k) = Fh(m)FH stands for the sub-carrier coupling matrix, which models the output/input relation between transmit and receive symbols in the frequency domain. Once channel estimates are available on OFDM symbol and sub-carrier with pilots, channel interpolation is needed in time and frequency domains for equalization purposes.
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