In doubly-dispersive channels condition,we have proved the bit error performance of LOFDM system much better than OFDM system.By combing Turbo equalization and the system of LOFDM,the paper proposes one T-LOFDM system on the condition of doubly-dispersive channels,and expatiates its work theory.Simulation results validate: in doubly-dispersive channels condition,the bit error performance of T-LOFDM system is much better than the system of LOFDM system combined with MMSE equalization,also much better than the system of OFDM system combined with Turbo equalization.

Inter-symbol interference(ISI) will be caused when Faster-Than-Nyquist(FTN) signaling is applied,and it will degrade the system performance according to the traditional communication theory.In 1975,however,Mazo told us that system performance will not be degraded as long as the transmission rate is not beyond 25% faster than the Nyquist rate,because the minimum euclidean distance is not changed though ISI exists.In this paper,a realization scheme in AWGN channel based on two-stage equalization for FTN transmission system is proposed,which is composed of a linear minimum mean square error(MMSE) equalizer followed by a windowed Chase equalizer.Simulation results show that the receive scheme can work normally and keep the BER performance invariable if the transmission rate is not beyond 25% faster than Nyquist,which validates the theory of Mazo through experiment.

In doubly-dispersive channels condition, we have proved the bit error performance of LOFDM system much better than OFDM system. The paper combines Turbo Equalization proposes one LOFDM Receiver structure (T_LOFDM) on the condition of doubly-dispersive channels, and expatiates its work theory. Simulation results validate: In doubly-dispersive channels condition, the bit error performance of T_LOFDM Receiver much better than the receiver of LOFDM system use MMSE equalization, also much better than the receiver of OFDM system use Turbo equalization.