Abstract-In this paper, we deal with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems. The channels are assumed to be time-varying (TV) and approximated by a basis expansion model (BEM). Due to the time-variation, the resulting channel matrix in the frequency domain is no longer diagonal, but approximately banded. Based on this observation, we propose novel channel estimators to combat both the noise and the out-of-band interference. In addition, the effect of a receiver window on channel estimation is also studied. Our claims are supported by simulation results, which are obtained considering Jakes' channels with fairly high Doppler spreads.Index Terms-Basis expansion model (BEM), orthogonal frequency-division multiplexing (OFDM), pilot-assisted modulation, time-varying (TV) channels.

No abstract

No abstract

No abstract

In orthogonal frequency division multiplexing (OFDM) systems, the pilot signal is inserted to obtain the channel state information (CSI). The time frequency interferometry (TFI) method reduces the number of pilot signals by using the real and null signals and obtains the accurate CSI by averaging the two time windows. On the other hand, many averaging operations are necessary to obtain more accurate CSI. Before now, we have proposed the pilot signal based on the imaginary and null signals. By using these characteristics, in this letter, we propose the real and imaginary TFI pilot signals to obtain the CSI from the four time windows averaging for OFDM systems. References [1] K. Higuchi and A. Benjebbour, "Non-orthogonal multiple access (NOMA) with successive interference cancellation for further radio access," IEICE Trans. [2] E. Okamoto, "Performance improvement of wireless multiple access scheme by interference division and superposition," TELECOM Frontier, no. 89, pp. 1-9, 2015. [3] K. Takeuchi, R. R. Muller, and M. Vehkapera, "Iterative LMMSE channel estimation and decoding based on probabilistic bias," IEEE Trans.