Key Technology In Physical Layer Of WiMAX System

With the growing requirement of voice services, data services and multimedia services in the wireless communication, high data rate, QoS and channel capacity are increasingly necessary, which promote people to improve the spectrum efficiency and stability of the link. So the development of broadband access network focuses on two trends as broadband and wireless. Broadband access technology is divided two parts: broadband wireless access and broadband wire access. Without the limitation of boring strings, BWA is attracting people's attention and becoming hotspot of communication technology. Worldwide interoperability for Microwave Access (WiMAX) is one of emerging BWA technology. Many equipment manufactures and service providers are favor of it because of its commercial opportunity.Orthogonal Frequency Division Multiplexing (OFDM) is one of three alternative technology of the physical layer of WiMAX. As one kind of modulation technologies of multi-carrier digital communication, it has the advantage of high spectrum efficiency and low multi-path delay spread. So it is considered to be one of potential technologies of the fourth generation mobile communications system. The main idea behind OFDM is to split the data stream to be transmitted into N parallel streams of reduced data rate and to transmit each of them on a separate sub-carrier. These carriers are made orthogonal by appropriately choosing the frequency spacing between them. Therefore, spectral overlapping among sub-carriers is allowed, since the orthogonality will ensure that the receiver can separate the OFDM sub-carriers. In order to get better performance, the synchronization of the system should be guaranteed. Meanwhile, frequency and time selective fading result from complex wireless mobile communication environment would degrade the performance of WiMAX system. So, this thesis takes a overall look at issues of synchronization and channel estimation.Under mathematical analysis of principle of synchronization and error resulting from synchronization bias, a scheme based on the preamble of IEEE802.16 is proposed to improve the synchronization. After robust synchronization is achieved, LS and LMMSE channel estimation methods are proposed and analyzed to remove the affect of changing channel. Both algorithms are tested under SUI channel model that IEEE 802.16 work group recommend. Results of simulation and analysis show considerable performance improvement in bit error rate and symbol error rate. Finally, all key algorithms are implemented in the hardware platform and some optimization methods are realized.