| The future wireless communication systems are expected to provide ubiquitous, high-quality, high-rate multimedia services and data transmission for all kinds of users using the minimum possible resources. However, hostile multi-path fading radio conditions give rise to serious inter-symbol interference (ISI), and frequency resources are quite limited. Orthogonal Frequency Division Multiplexing (OFDM), which is inherently resistant against ISI, with high bandwidth efficiency and flexible modulation modes, has caused popular attention recently, and has been a key technology of the physical layer for future wireless communications. Notwithstanding, OFDM is much more vulnerable to errors of synchronization and channel estimation, and how to obtain correct synchronization and channel estimation efficiently is highly critical to OFDM systems.Firstly in this dissertation, the development of wireless communications, wireless channel models and the system model of OFDM are introduced. Secondly, based on discussion about principles of channel estimation, the performance, complexity and suitable environments of different estimation algorithms, different pilot schemes and different interpolation methods are summarized and compared. Then an improved channel estimation method using least mean square adaptive filter algorithm together with least square channel estimation is proposed. Simulation results and mathematical analysis show that this method reaches good balance between performance and complexity. Thirdly, based on discussion about effects of synchronization errors, different synchronization algorithms are compared and analyzed. Then, an improved method for carrier offset synchronization using phase locked loop is proposed, and simulation results show that it is better in performance than traditional methods. Finally, based on research about physical layer standards of IEEE 802.11a, a simulation platform of transmitters and receivers using Matlab is built, and the whole performance of baseband receiver algorithms in Wireless Local Access Network (WLAN) systems is analyzed. |
PDF Full Text Request