CHANNEL ESTIMATION FOR OFDM SYSTEMS BASED ON COMB-TYPE PILOT ARRANGEMENT IN FREQUENCY-SELECTIVE FADING CHANNELS

In this paper, the channel estimation methods for OFDM systems based o n comb-type pilot sub-carrier arrangement are in vestigated. The chann el estimation algorithm based on comb-type pilots is divided into pilo t signal estimation and channel interpolation. The pilot signal estima tion based on LS or MMSE criteria, together with channel interpolation based on piecewise-linear interpolation or piecewise second-order pol ynomial interpolation is studied. Owing to the MMSE estimate of pilot signals, the inter-carrier interference and additive white Gaussian no ise are reduced considerably. The computational complexity of pilot si gnal estimation based on MMSE criterion can be reduced by using a simp lified LMMSE estimator with low-rank approximation using singular valu e decomposition. Phase compensators before and after interpolation are also presented to combat the phase changes of subchannel symbols aris ing from the frame synchronization errors. Comparing to the transform- domain processing based channel estimation algorithm, the MMSE estimat e of pilot signals together with phase compensated linear interpolatio n algorithm provides better performance and requires less computations .