Inter-Channel Interference Mitigation for Mobile OFDM Systems
Kuan Lin Chen
Hsiang Feng Chi
Yu Ted Su
In the recent years, OFDM has become one of the most popular transmission technologies for broadband wireless communication systems because of the ability of combating Inter-Symbol Interference(ISI) in the frequency selective channel and the excellent bandwidth efficiency. However, when OFDM systems are applied in the high speed mobile applications, the channel time-variation, the namely time selectivity in a symbol duration introduces Inter-carrier interference (ICI), which destroys the orthogonal property between sub-carriers. ICI will become severe when the mobile speed, the carrier frequency, and the symbol duration increase. Without solving this problem, the receiving performance will be degraded, and the bit error floor will appear even in the high SNR condition. The previously published method of solving the mobile ICI problem is composed of the parallel interference cancellation (PIC) and the time-varying channel frequency response reconstruction (estimation). The reconstruction is based on piece-wise linear interpolation in time. But, in the high mobility wireless receiving, the piece-wise linearity assumption of channel response will be not true. Using the piece-wise linear interpolation for channel estimation cannot obtain satisfactory performance in the high mobility condition. In this thesis, we propose three interpolation algorithms for mobile channel reconstruction. They are the second order interpolation, the low-pass filter interpolation, and the Wiener filter interpolation. The simulation results show that the proposed methods are better than the previously published method especially at high SNR. Utilizing the information of channel correlation matrix, the Wiener filter can provide the best performance.