On Synchronization Algorithms For Orthogonal Frequency Division Multiplexing Systems In Multipath Fading Channels

The next generation mobile communications systems (Beyond 3G) will make effort for broadband wireless access to achieve high data rate, high quality and effective transmission. To achieve high data transmission (such as 100 Mbps in mobile environment), the system bandwidth (50~100MHz) would be much larger than that of 3G system. In such a broadband system, the number of resolved multipaths would be very large and the traditional code division multiple access (CDMA) system would encounter severe multipath interference. Even by Rake receiver, the multipath energy also can't be used effectively. Orthogonal Frequency Division Mutiplexing (OFDM) can well solve such problem, which uses many low rate subcarriers to achieve a high data rate transmission. The cyclic prefix (CP) is introduced to eliminate the multipath interference and the channel frequency diversity gain can also be effectively obtained. Small symbol timing offset and accurate frequency synchronization is the precondition for OFDM system to properly work. Aimed at beyond 3G mobile system, the dissertation has investigated the synchronization algorithms for OFDM based systems in multipath fading channels comprehensively and in depth. And some creative works have been done as follows.1. On the influence of synchronization error to OFDM system performanceThe reasons of resulting in inter-carrier interference (ICI) in OFDM system have been investigated comprehensively. And the effect of synchronization shift to OFDM system performance has also been investigated by simulations.2. On the synchronization algorithms in OFDM downlinkThe existing synchronization algorithms in OFDM downlink system have been investigated comprehensively. After the analysis of the bad performance of CP based algorithms in multipath fading channels, two enhanced shemes have been proposed to improve its performance.3. On the synchronization algorithms in OFDMA uplinkThere is multi-user interference in OFDMA uplink system. Because one OFDMA symbol contains many users' signals, the synchronization for OFDMA uplink system would be more challenging than downlink scenario. After having analysed the characteristic of different subcarrier assignment schemes, the symbol timing estimators have been proposed for block and interleaved OFDMA uplink system...