| Summary: | 碩士 === 國立清華大學 === 通訊工程研究所 === 95 === Orthogonal frequency division multiplexing (OFDM) has been widely adopted in the next generation wireless communication systems. A major disadvantage of OFDM systems is the sensitivity to the frequency offset, which is usually caused by mismatch of the oscillators between the transmitter and the receiver or the Doppler effect. The frequency offset will destroy the orthogonilty among subcarriers and then introduce intercarrier interference (ICI), which degrades the system performance dramatically. Several methods have been proposed to combat the ICI effect in the OFDM systems. One of the simple and effective methods is the ICI self-cancellation scheme, but the spectral efficiency is half of the standard OFDM system. On the other hand, ICI can be handled by performing correlative coding in frequency domain. However, such correlative coding schemes could only perform well in BPSK modulation. When higher order modulation scheme is used, the performance would be sdegraded significantly.
In this thesis, we propose a new ICI suppression scheme that can be regarded as an improved version of the correlative coding approach. The intention of our approach is to overcome the high bit error rate (BER) situation occurring in the conventional correlative coding scheme due to the severe error propagation problem when high order modulation is chosen. To achieve this goal, we transmit real and imaginary part of correlative coding signals separately. Simulation results show that the proposed scheme not only keep the immunity against ICI, but also mitigate the severe error propagation in the conventional correlative coding scheme when high order modulation is used.
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