CHANNEL ESTIMATION FOR WCDMA SYSTEMS USING EM AND MMSE-ML TECHNIQUES

Abstract

CDMA is the multiple access technique selected for the 3G mobile communications systems and it has a significant role in the research beyond 3G systems. CDMA systems over wireless channels have to cope with fading multi-path propagation, which makes the channel estimation an important issue in CDMA receivers. Despite a significant amount of scientific literature on CDMA receivers, there are still open problems regarding the multi-path channel estimation. The -work presented in this thesis is focused on three main problems: MMSE-ML channel estimation algorithms for WCDMA model, Expectation Maximization technique and Baum Welch algorithm for Channel estimation. In this dissertation work, we first discuss the WCDMA channel model, RAKE receiver, need of channel estimation in RAKE receiver and MMSE-ML channel estimation technique for WCDMA model with the main focus on the delay estimation and gain estimation. After this, we discuss Expectation Maximization technique and then we consider the application of EM for data detection in multi-user case. Channel estimation algorithms for single user single tap channel and single user multi-tap channel for WCDMA model are introduced. Next channel gain estimation algorithm for WCDMA model using Baum Welch and EM technique for multi-user multi-tap channel is presented. The last part of this thesis is a collection of flow charts, various simulation results and graphs