Design of an Adaptive OFDM System for Mobile Wireless Communication
Date Issued
2008
Date
2008
Author(s)
Lin, Jun-Wei
Abstract
This thesis proposes design of an adaptive OFDM system with new enhanced adaptive OFDM techniques and extends OFDM application to mobile wireless communications. When compared to conventional OFDM systems, the proposed adaptive OFDM system achieves great performance improvement, especially in high mobility operation. In mobile wireless communication application, in addition to adaptive modulation, feedback reduction and channel prediction, intercarrier interference (ICI) all need to be taken into account. Considering all issues above, I propose several novel techniques and develop an integrated adaptive OFDM system solution. At first, a dynamic threshold bit-loading algorithm is proposed for adaptive modulation; then an adaptive differential coding on pilot is proposed for feedback reduction; and an iterative RLS algorithm is proposed for channel prediction with better precision. Furthermore, in order to combat the notorious ICI problem in mobile environments, adaptive pilot power and adaptive symbol duration algorithms are proposed. ICI cancellation equalizer is also included in the proposed system. For the completeness of this work, methods for Doppler frequency estimation and SNR estimation are also proposed. Simulation results using the ITU-R vehicular channel model show that the proposed system can effectively combat multi-path Rayleigh fading and Doppler effect and successfully mitigates the error floor problem often encountered in high mobility scenarios.
Subjects
adaptive OFDM
mobile wireless communication
adaptive modulation
channel prediction
ICI
Type
thesis
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