Expectation-Maximization Algorithm based Channel Estimation for OFDM System

Abstract

Multi-carrier modulation, in particular Orthogonal Frequency Division Multiplexing (OFDM), has been successfully applied to a wide variety of digital communications applications over the past several years. Although OFDM has been chosen as the physical layer standard for a diversity of important systems, the theory, algorithms, and implementation techniques remain subjects of current interest. This is clear from the high volume of papers appearing in technical journals and conferences. Orthogonal frequency division multiplexing (OFDM) has been shown to be an effective technique to combat multi path fading in wireless channel. It has been and is going to be used in various wireless communication systems. This Thesis gives a comprehensive introduction on the theory and channel estimation algorithms for OFDM systems. Estimating a channel that is subject to frequency selective fading is a challenging problem in an OFDM system. We shall discuss the three EM-based algorithms to efficiently estimate the channel impulse response (CIR) or channel frequency response of such a system operating on a channel with multi path fading and additive white Gaussian noise (AWGN). OFDM systems require an efficient channel estimation procedure to demodulate the received data coherently. The performance characteristics of different algorithms (LMS, MMSE,EM,EMMMSE, QUASI-NEWTON ACCELERATION ) have been developed and compared. Statistical analysis of adaptation characteristics aforementioned algorithms.