Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Wireless communications

The WiMAX Physical Layer Based on OFDM as a Key of Technology Research

Author YaMiDi(Jean-Baptiste Yamindi)
Tutor WuMuQing
School Beijing University of Posts and Telecommunications
Course Communication and Information System
Keywords Pilot Hexagonal Pilot Rectangular Pilot Virtual pilot Channel Estimation Iterative Detection
Type PhD thesis
Year 2010
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As people’s demand for broadband wireless communication is increasing, which means demand for higher speed, greater coverage, and better mobility. The Worldwide Interoperability for Microwave Access(WiMAX) technology, is just to satisfy user’s demand for wireless communications. The OFDM system applied to the WiMAX network, a combination of the characteristics of wireless communications and the Internet to adapt to the market and technology trends, become the next generation of wireless communication network’s critical technologies.The Wireless mesh networks research is based on the wireless local area networks (IEEE 802.11s) and wireless metropolitan area network (IEEE 802.16). The Wireless mesh network is the combination of Mobile Ad Hoc Networks, (MANET) and Wireless Local Area Networks (WLAN) that gave birth to the gradual development of a new network technology.This thesis focuses on the new Genetic Algorithm-Aided iterative Joint Channel Estimation and Multi-User Detection (GA-JCEMUD) and analysis of the OFDM system of signal transmission on the WiMAX Physical layer, the Space Division Multiple Access-Orthogonal Frequency Division Multiplexing (SDMA-OFDM) systems is used for channel estimation based on Minimum Mean Square Error (MMSE) and the pilot-assisted channel transfer function estimation and the Multiple-Input Multiple-Output (MIMO) structure of the channel of the multi-user single transmitter antenna scenario using multiple transmitter antennas.This drawn wide research interests in-depth studies and in my research, I have done the following innovative works:1. Research on the analytical technique of pilot-assisted classification based on Decision-Directed (DD) and Blind Channel Estimation (BCE). The Pilot-Assisted channel transfer function estimate receives a particular pilot signal, which can be a subset of subcarriers, that is used in a particular channel transfer function as a sample. In this thesis, using different methods to produce a pilot sub-carrier for each of the transfer function estimation method to improve the channel estimation accuracy and reduce the complexity of the original algorithm.2. Based on the joint iterative channel estimation method proposed a more advanced SDMA-OFDM system channel estimation method, which combined Genetic Algorithm-Aided Iterative Joint Channel Estimation and Multi-User Detection (GA-JCEMUD), so that the proposed algorithm can effectively solve the multi-user channel estimation problem.3. Proposed a new Cartesian Mathematical analysis concept of the Hexagonal Pilot Pattern, Hexagonal with Virtual Rectangular Pilot and Rectangular with Virtual pilot. It presents the application of the Cyclic Prefix (CP) to resolve the inter-symbol interference and the two different processes of the performance of 2D-FIR Wiener filter for the channel estimation. The central focus of the work is the comparison of the pilots and the approach of the better performance of the Hexagonal Pilot Pattern distribution with the support of Cellular Network configuration.In this Thesis, Genetic Algorithm-based iterative Joint Channel Estimation and Multi-User Detection (GA-JCEMUD) technique, through the initial Frequency Domain CHannel Transfer Function (FD-CHTF) and the initial symbol estimates to deal effectively with the growing number of users. Since the algorithm is the soft output of the method proposed to solve the channel estimation and Multi-User Interference (MUI) problem in the received signal, the channel state information can be calculated by the probability of a candidate with higher transmission vector.The Hexagonal pilot pattern is one of the best examples, which represent the same signal with the rectangular pilot model of lower than 13.3% of the samples and with improved bit error rate performance. The Interference effects of multiple scattering analysis and proposed hexagonal pilot model programs on the validity of the analysis.The simulation results obtained using mathematical theory shows that the design is superior to a rectangular hexagonal pilot and other forms of pilot mode such as the hexagonal pilot, hexagonal with virtual pilot.Therefore, by undergoing the processes above, the WiMAX physical layer of the OFDM symbols for the channel estimation performance model is simulated and an improved performance result is thus obtained.

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