Study On The Key Technology Of OFDM Transmission System Based On IEEE802.16d

OFDM (Orthogonal Frequency Division Multiplexing) is amulti-carrier modulation method. Since OFDM can lessen the severeeffects of frequency selective fading and improves the spectrumefficiency, it has been widely used in the fields of digital audiobroadcasting, digital television and wireless local area networks and hasbeen indicated to become a key technology in the Fourth Generationmobile communications.However, one of the drawbacks of OFDM is the sensitivity tosynchronization error, especially to frequency offset. When asynchronization error exists, the orthogonality between sub-carriers can'tbe maintained, serious inter-carrier interference is introduced anddemodulation performance will be degraded greatly. So, perfectsynchronization methods are essential to OFDM system. Similar to otherOFDM-based systems, the physical layer of IEEE802.16d system hasfour kinds of the synchronization methods including frame synchronization, symbol synchronization, carrier synchronization andsampling synchronization. In addition, multipath fading and channelvolatility will influence system's performance and therefore channelestimation is also important.This thesis will discuss all the four kinds of synchronization methods.It studies, analyses, compares some synchronization methods andimproves them to meet the needs of IEEE802.16d system. After analyzingthe IEEE802.16d protocol, we propose a new method for CFO estimationvia oversamping for OFDM systems and a new method for timingrecovery in ISI channels. The simulation platform of the physical layer ofIEEE 802.16d system using MATLAB is given and many simulations aretaken, the performances are given by simulation results, and someconclusions are given. The simulation results show that the new methodscan work well under low SNR environment.In addition, this thesis also studies the channel estimation methodsof the OFDM system of IEEE802.16d. It mainly focuses on the channelestimation methods of the OFDM systems such as LS (Least square)estimation criterion based on comb-type pilot assignment, LMMSE(linear minimum mean squared error) estimation criterion based on basedon comb-type pilot assignment and LMMSE estimation criterion basedon block-type pilot assignment. The performance and application of thedifferent methods are compared. It shows that the channel estimation criterion based on block-type pilot assignment is more suitable inIEEE802.16d system.Zhu Wen (Communication and Information System)Supervised by Qiu Runhe...