Cyclostationarity-Based Maximal Doppler Spread Blind Estimation for LOFDM Systems in Doubly-Dispersive Channels

LOFDM (Lattice Orthogonal Frequency Division Multiplexing), which is proposed by Strohmer T and Beaver S in 2003, has higher spectral efficiency and better bit error rate (BER) performance compared with OFDM systems in the time-frequency dispersive channel. To minimize the joint inter-symbol interference (ISI) and inter-carrier interference (ICI) caused by the doubly dispersive channel, LOFDM systems need to adapt the parameters of signals’ TFL and shaping-pulse scale to the channel dispersion characteristics in the transmitters. The maximal Doppler spread, or equivalently, the mobile speed, is a measure of the spectral dispersion of mobile fading channel. Accurate estimation of the mobile speed is of importance in LOFDM systems which require the knowledge of the rate of channel variations to achieve its adaptive strategy. In this paper, aiming at the special characteristics of LOFDM signals, a cyclostationarity-based blind maximal Doppler spread estimation algorithm for LOFDM systems over the doubly-dispersion channels is proposed, which avoids the waste of spectral efficiency in the current estimation algorithms. Theory analyses and simulation results demonstrate that the proposed algorithm can obtain the effective estimation for a wide range of Doppler spreads under the condition that the information of the multi-path is unknown and have a good normalized mean square error (NMSE) performance, while both the capability of anti-noise and the speed of convergence are nice.