Research On Channel Estimation Of OFDM System With Applications To DVB-C2System

In such an era that is highly information-oriented, the demand for mobilecommunication technology is not restricted in voice communication. People arecommitted to the development of an advanced communication system which has greateruser capacity, faster transmission rate, higher spectrum efficiency and more abundantdata services. OFDM technology plays a significant role in the developing process ofmobile communication technology benefited from its high spectrum efficiency andoutstanding resistance to the influence of multipath time delay. Channel statusinformation is necessary at the receiver side of the OFDM system in which coherentdemodulation is applied. The accuracy of channel estimation is a crucial factor toevaluate the performance of the system. Therefore, the research of channel estimation isof great importance.This thesis focuses on channel estimation algorithms in OFDM system. Theresearch consists of pilot-symbol-aided channel estimation and time domain PNsequence correlation based channel estimation.Firstly, time domain PN sequence correlation based channel estimation is discussed.TDS-OFDM system is overviewed. The emphasis of the description is the unique framestructure which is needed by the time domain PN sequence channel estimation. Then,the thesis briefly describes the remarkable correlation characteristic of PN sequence andthe classical methods of time domain channel estimation and points out that theaccuracy of the classical channel estimation methods will be influenced by ISIinterference which is very serious in the long time-delay multipath channel. To solvethis problem, an iterative subtraction channel estimation method which can make theperformance of the system1-3dB higher is proposed and verified in simulation.Then the thesis focuses on the pilot-symbol-aided channel estimation. After thebrief discussion of the pilot pattern and the channel estimation at the position of pilotsymbols, classical interpolation algorithms are analyzed in detail. On the basis of theintroduction of traditional interpolation algorithms, the thesis proposes that the classical interpolator can be designed as a series of poly-phase sub-filters. Based on theequivalence between frequency interpolating and time-domain windowing, the filterdesign methods are employed to develop a complex low pass interpolator whichenhancing the robustness of channel estimator against long-delay echoes. The designedinterpolator and classical interpolation algorithms are verified in a simulated DVB-C2receiver. The simulation results indicate that the designed channel estimator has goodresistance to the long-delay echoes in the channel.