Research On Channel Estimation Technique Based On Pilot For OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is a high-speed multicarrier transmission techlonogy in wireless communications, and it has been regarded as the core technology of 4G mobile communication systems due to its high bandwidth efficiency and robustness combat multipath interference. Channel estimation techlonogy is one of the most important research hotspot in OFDM systems.In the channle estimaion based upon pilot signals, the channel response in time-domain or frequency-domain is eastimated firstly and used in detection, subcarrier power allocation, equalization and adaptive modulation of OFDM systems.This dissertation firstly introduces the principle and performance characteristics of OFDM and analyzes the wireless channel. The multipath and time-varying statistic properties of the wireless fading channel are summarizesd, the model and simulation method of flat fading channel and frequency-selective fading channel are established respectively.Aiming at the OFDM system,the system performance influenced by channel properties,especially multipath fading and Doppler shift are analyzed.Based on these analysis, the block-pilot and comb-pilot arrangement of OFDM systems are analyzed and researched. Several interpolation algorithms to acquire the entire channel frequency responses are discussed and simulated in different fading channel, such as linear interpolation, second-order interpolation, spline interpolation, transform domain interpolation and so on.The simulation results indicate that the block-pilot scheme adapts to slow fading channels, while both flat fading and selective frequency fading have a little infection on it. On the other hand, the comb-pilot scheme is expected to have better performance in flat fading channels, while both slow fading and fast fading have a little influence on it. In addition, the transform domain interpolation performs better than the other interpolation algorithms. According to transform domain interpolation algorithm based on comb-pilot scheme, the dissertation proposes an improved transform domain interpolation method. Simulation results show that the proposed method earns ~2dB E_b/N_o gain than the conventional ones. Finally, the adaptive channel estimation technology is researched,simulation results show that the adaptive channel estimation can achieve higher spectral efficiency.