| Summary: | 碩士 === 國立交通大學 === 電信工程系所 === 97 === Orthogonal frequency division multiplexing (OFDM) is an attractive transmission technique, which effectively deals with the delay spread of the multi-path channel by appending a cyclic prefix (CP) in every OFDM symbol. However, the necessary insertion of CP produces a transmission overhead and reduces the throughput of the communication systems. A direct reduction of CP can improve the spectral efficiency but also introduces the undesired inter-symbol interference (ISI) and inter-carrier interference (ICI), hence limiting the overall system performance. To enhance the performance of the CP-shortened OFDM system, the CP-reduced coding techniques with ICI diversity combining for OFDM systems are studied here. Actually the ICI corrupted channel of the CP-reduced OFDM system can be viewed as a virtual MIMO channel when we regard the subcarriers as the virtual antennas. And the ICI induced by insufficient CP can be viewed as a sort of frequency diversity by the concepts of space-frequency coding (SFC). In this thesis, we investigate the virtual space-frequency coding techniques based on the effective MIMO channel of the CP-reduced OFDM system and propose the corresponding design criteria to develop good virtual space-frequency codes. The maximum achievable diversity order of the virtual space-frequency code is determined by the theoretical analysis. Simulation results are also provided to show that the proposed coding schemes not only achieve higher diversity order to enhance the error performance but also have higher data rate compared with the conventional coded OFDM systems.
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