Low-complexity constrained LMMSE estimator for the sparse OFDM channels

In this article the constrained linear minimum mean squared error (CLMMSE) algorithm is presented for the multipath channel response estimation in the OFDM systems using equispaced and equipowered pilot subcarriers. It relies on tracking of the channel correlation and signal-to-noise ratio and has a low computational complexity due to the transform-domain processing and no matrix inversions required. The proposed algorithm exhibits a substantial performance improvement for the sparse channels (9 dB in MSE and 1.4 dB in BER), whereas for channels with the dense impulse responses its accuracy is equivalent to the LMMSE scheme with the robust design parameters.