Channel estimation for OFDM systems based on comb-type pilot arrangement in frequency selective fading channels

The channel estimation methods for OFDM systems based on a comb-type pilot sub-carrier arrangement are investigated. The channel estimation algorithm based on comb-type pilots is divided into pilot signal estimation and channel interpolation. The pilot signal estimation based on LS or MMSE criteria, together with channel interpolation based on piecewise-linear interpolation or piecewise second-order polynomial interpolation is studied. Owing to the MMSE estimate of the pilot signals, the inter-carrier interference and additive white Gaussian noise are reduced considerably. The computational complexity of pilot signal estimation based on MMSE criterion can be reduced by using a simplified LMMSE estimator with low-rank approximation using singular value decomposition. Phase compensators before and after interpolation are also presented to combat the phase changes of subchannel symbols arising from the frame synchronization errors. Compared to the transform-domain processing based channel estimation algorithm the MMSE estimate of pilot signals together with phase compensated linear interpolation algorithm provides a better performance and requires less computations.