Pilot-Symbol-Aided Channel Estimation For OFDM Systems And Its Application In 802.16e

Due to its features of multipath immunity and bandwidth efficiency, OFDM (Orthogonal Frequency Division Multiplexing) has been favored for IEEE 802.16e, which is the newly published standard for fixed and mobile broadband wireless access systems, and has become a prime candidate for next generation mobile communications systems. The requirements for IEEE 802.16e mobile broadband wireless access systems such as high data rate, high quality and high mobility make channel estimation and channel tracking techniques more important. Hence this thesis mainly focuses on channel estimation and its application in IEEE 802.16e systems.Firstly, channel estimation in fixed broadband wireless access systems is discussed. We give their performance comparison of some conventional pilot-symbol-aided channel estimation algorithms in SUI channels which are typically slow fading. Further, a DFT-based channel estimation algorithm for systems with virtual carriers is proposed. We present LS method to estimate the CTF at virtual pilots by exploiting the estimated CTF of pilots. Simulation result shows that the DFT-based channel estimator incorporating the CTF estimation at virtual carriers performs well with low complexity.Secondly, for the SUI testing channel models of fixed broadband wireless access systems, we present a model-based judging method which can make a decision of current channel profile via limited estimated samples. As a correct decision is made, a matching MMSE estimation algorithm is applied to OFDM systems. Afterwards, a residual phase correction mechanism for the specific subframe structure of WiMAX-OFDM system is investigated. It gives a better tracking performance than the time-domain linear interpolation.Finally, channel estimation in mobile broadband wireless access systems is taken into our account. We analyse the channel estimators for nonsample-spaced channels where aliased spectral leakage exists. Based on this, an improved DFT-based estimation algorithm is designed by pre-shifting the channel impulse response right. Compared to the direct-DFT method, it has been simulated and proved to be high-efficient and avoids the occurrence of error floor caused by aliased spectral leakage with nearly equal complexity in nonsample-spaced channels.