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Study on Diversity Application of OFDM System in Fast Fading Channel

Author: JingMei
Tutor: QianLiang
School: Shanghai Jiaotong University
Course: Communication and Information System
Keywords: OFDM fast-varying channel interference self-cancellation Doppler diversity
CLC: TN919.3
Type: Master's thesis
Year: 2008
Downloads: 8
Quote: 2
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Abstract


Due to the high spectrum efficiency, ease of implementation (via FFT), and low receiver complexity (single-tape equalization) and so on, orthogonal frequency division multiplexing has been adopted and is currently considered by many application standards, including digital audio and video broadcasting (DAB, DVB) in Europe, high-speed ADSL modems over twisted pairs in the United States, wireless LAN technology standards IEEE802.11a, broadband wireless access technology standards, and the fourth generation mobile system.The sensitivity to frequency offset in OFDM system has become a primary problem to solve for its system design. The frequency offsets include both the frequency offset of the local transceiver and Doppler frequency shift in time-varying multi-path channel. In particular, the system frequency will become higher, the number of sub-carriers will become bigger and the speed of the users will become faster in the future OFDM wireless communication systems, which will lead to more Doppler frequency shift. Frequency Offset destroys the orthogonality between OFDM sub-carriers, and then generates ICI, which lead that the system performance is decreased obviously.This thesis analyzed the ICI influence to the OFDM system of two kinds of the frequency offset, and summed up their laws of the changes. Based on the analysis of Zhao’s ICI self-cancelation algorithm and its improved algorithm, this paper proposes an algorithm that optimizes the transceiver weight factors, which greatly enhances the system performance. And then the realization of the transmitter has been optimized.Doppler spread destroys the orthogonality between OFDM sub-carriers. But at the same time,Doppler spread brings usable resources. Doppler diversity at the receiver studied for Doppler spread is obvious in high- speed mobile environments. Then a novel simp1ified Doppler diversity technology for OFDM is analyzed. Following that,the optimal configuration of the simp1ified Doppler diversity receiver is put forward.

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