An ISI Transmission and the Optimal Detection/Decoding of the Coded ISI System

A high-speed transmission of the lower-order modulated signals that would bring intersymbol interference (ISI) is researched. At the receiver of the new system, oversampling and the maximum likelihood sequence detection(MLSD) is used. Under the same spectral efficiency, the bit error rate performance of the new system is compared with that of high-order modulated symbol-by-symbol transmission. It is concluded that the new system utilizing MLSD detector could make full use of the inherent anti-jamming capability of the system and outperform the non-ISI symbol-by-symbol system. The optimal soft-in soft-out ISI detection joined with the decoding is proposed for the channel coded ISI system. Under the maximum a posteriori probability (MAP) criterion, the soft information is passed iteratively between the detector and the decoder. Simulation results show that the optimal performance is obtained because of the encoding constraining naturally formed by ISI.