Study of IEEE 802.16a TDD OFDMA Uplink Channel Estimation

• Main Authors: Ming-Je Li, 李明哲
• Other Authors: David W. Lin
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/f2je28

碩士 === 國立交通大學 === 電子工程系所 === 92 === In recent years, orthogonal frequency division multiplexing (OFDM) modulation technique has drawn great interest due to its advantage in mitigating the severe effects of frequency-selective fading in high-speed wireless communication. And the IEEE 802.16a standard is a wireless metropolitan area networks standard based on OFDM technique. The goal of this thesis is to estimate the uplink channel with sufficient accuracy according to the time-division duplexing (TDD) orthogonal frequency division multi-access (OFDMA) specifications in the standard so that the transmitted data can be detected even when a large constellation is used. However there are only 5 pilot carriers within a subchannel to estimate the channel in the IEEE 802.16a OFDMA uplink. That strict condition makes the conventional channel estimation useless. We develop a suitable algorithm under the assumption that we know the delay information. Firstly, the least square estimator roughly estimates the channel. Then by using the linear combination between decision-directed and least squares estimators, the noise power is effectively reduced in low SNR. Moreover, we use an adaptive filter to trace the time-variant channel along the time axis so that we get better performance in high SNR. The decision-directed estimator is used as the final stage. It can further reduce the noise power and get more accurate channel estimate. Finally the proposed estimator can achieve significant performance improvement over the least squares estimator about 7-8 dB in a multipath time-variant environment. According to our simulations, the proposed estimator works well whether multipath time delays are at sample spaced positions or not. It is also robust under various multipath intensity profiles. For only one user, the ICI effect is not serious and just causes a little performance degradation in high SNR.