Studies on Equalization and Channel Estimation in Ofdm over Doubly-selective Channel

Orthogonal Frequency Division Multiplexing (OFDM) is a hotly researched topic, due to its high data rate and robustness to multi-path fading. As such, it has been widely adopted in wireless standards, e.g., IEEE 802.11a/g, digital audio/video broadcasting and Integrated Services Digital Broadcasting (ISDB). In the presence of doubly-selectivity in fading channels, OFDM suffers from intercarrier interference (ICI) and inter-symbol interference (ISI). To counteract the effects of ICI and/or ISI, channel state information (CSI) is needed for equalization. However, when there are time variation and multipath fading, the number of unknown channel variables exceeds the number of known transmitted symbols, making it diff icult to obtain CSI. Thus, the need to finitely parameterize the channels by a smaller number of variables arises. This stimulates the development of f inite parameter model for channel modeling which can also be used to aid channel estimation. In Chapter 2 of the thesis, to describe the doubly-selective channel in mobile broadband wireless communications, we propose the use of a finite parameter model based on the same Bessel functions for each tap (Bessel model). An expression of channel estimation mean squared error (MSE) based on the f inite parameter models in OFDM systems is derived. Then, our Bessel model is compared with commonly used finite parameter models in terms of the channel estimation MSE. Even if Research Engineer, Defense Science Organization National Labatories, Advanced Communication Labatory