STUDY OF CHANNEL ESTIMATION ALGORITHMS FOR OFDM BASED WIMAX 802.16 SYSTEMS

Abstract

Fixed broadband wireless access systems, covered by the IEEE standard called

IEEE802.16, require high bit-rate, reliable and power efficient transmission systems.

It supports the Orthogonal Frequency Modulation (OFDM) schemes as an optional

PHY layer.

OFDM has been recognized as a powerful multi-carrier modulation technique that provides efficient spectral utilization and resilience to frequency selective fading channels. OFDM is used to reduce the ISI and to avoid using very complex equalizer at high bit rates.

In OFDM link, modulated bits are distributed during the transmission through the channel since the channel introduces amplitude and phase shifts due to frequency selective and time-varying nature of the radio channel. In order for the receiver to acquire the original bits the receiver has to know the transfer functions of the different sub-channels and time instants in order to enable coherent demodulation. Channel estimation allows the receiver to approximate the effect of the channel on the signal. The channel estimate is essential for removing inter symbol interference, noise rejection techniques, etc. Also used in diversity combining, ML detection, angle of arrival estimation, etc.

In this thesis, we analyze the physical layer ofWiMax (802.16) system. A study of the transmitter and the receiver is also given. We apply different channel estimation techniques on the system. This study is followed by various simulations where the behavior of the transmitter and the receiver is shown and the different channel estimation techniques are compared from the performance point of view. A WGN, Rayleigh fading channel models are considered in the system model.