Frequency smoothing gains in preamble-based channel estimation for multicarrier systems

In this paper, the problem of least-squares (LS) preamble-based channel estimation in multicarrier systems under a deterministic channel assumption is revisited. The analysis is presented for the filterbank multicarrier offset quadrature amplitude modulation (FBMC/OQAM) system, although the derived results hold unchanged for the cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) system, as well. Assuming independent noise disturbances per subcarrier, we show that frequency-domain smoothing techniques can be used to improve the mean square error (MSE) performance. Depending on the number of subcarriers, the choice of smoothing may be different. We also present the time-domain formulation of the frequency-domain smoothing. Based on this formulation, we show that frequency-domain smoothing techniques can minimize the variance of the LS channel estimator, while they can further reduce its MSE by trading bias for variance. Simulations are given to support the derived results.