Research On Channel Estimation Of Ofdm-Based System

In this dissertation we focus on the research of channel estimation of OFDM-based system, including the channel estimation of cooperative communication system and compressive channel estimation technology.At the beginning, we briefly introduce OFDM technology, the development of cooperative communication system and its application in 3GPP LTE-Advanced system.In chaper 2, we mainly introduce the channel estimation technologies and channel models of OFDM system. Firstly, ray-based model and correlation matrix based model are introduced for SISO and MIMO systems, and then followed by the performance analysis on smart antenna with mono-and dual-polarization in TD-LTE system. At last the classical LS, LMMSE and DFT algorithms are evaluated in 3G LTE systems, and the simulation results show they are sensitive to pilot density, pilot pattern, and Doppler spread.The introduction of relay in cooperative communication systems brings more challenges for channel estimation. In chapter 3, we study the channel estimation and pilot design in cooperative communication systems, including the channel estimation method under two different cooperative protocols (the amplify-and-forward and decode-and-forward). Then we design the uplink preamble and backhaul link reference signal for 3GPP LTE-Advanced system.Compressive sensing method can greatly reduce the pilot desity of channel estimation by exploiting the sparsity of channel in delay and Dopper domains. In chapter 4, we investigate the compressive channel estimation technology, and evaluate BP and OMP algorithms in different pilot density and pilot pattern, and compare with the classical LS/LMMSE method.In chapter 5, we summarize the whole dissertation and discuss the future research direction of channel estimation for OFDM systems.