Research On Bandwidth Efficient OFDM System

Space-time coding and orthogonal frequency division multiplexing (OFDM) are two core techniques in modern mobile communication. The combination of them is more powerful in improving the performance of system. This thesis concerned with the study of space-time block-coded OFDM system (STBC-OFDM). Space-frequency block-coded OFDM system (SFBC-OFDM) is developed from it. The method to improve the bandwidth efficiency of them is discussed.A channel simulation model is constructed and simulation result is given. The further study is given to space-time codes simulation and OFDM system design. The performance difference of space-time block codes in different condition is compared by computer simulation. By combining the space-time coding and OFDM modulation techniques, the STBC-OFDM system is introduced. It has been shown that the STBC-OFDM system is capable of achieving nearly optimum spatial diversity performance in slow fading frequency selective channels. By applying space-time block codes across the subcarriers of OFDM, the SFBC-OFDM system is developed. Simulation results have shown that SFBC-OFDM can achieve the same diversity performance as STBC-OFDM in slow fading frequency selective channels, but it outperforms STBC-OFDM in fast fading channels. Because the two systems have low bandwidth efficiency, tail cancellation and cyclic reconstruction and the iterative techniques are applied to the two systems. Simulation results have shown the iterative SFBC-OFDM and STBC-OFDM systems achieve nearly the same performance with the system with cyclic prefix and significantly improve bandwidth efficiency.