Study On Key Techniques And Application Of OFDM System

The future mobile communication system needs to offer the high-quality broadband business to various kinds of users, serious inter-symbol interference that multi paths delays cause limits improvement of transfer rate in high-speed data transmission. In recent years, Orthogonal Frequency Division Multiplex (OFDM) technique gets the extensive concern of the industry because of its ability of resisting inter-symbol interference. At present, realizing signal process of OFDM with modern digital signal process in order to receive good system performances is a hot research problem. In the dissertation, researching the defects that Peak-to-Average Ratio (PAR) is high and influenced greatly by frequency offset and time-varying channel in OFDM system, providing the effective settlement measures. The paper assigns as follow: On the problem of reducing the high Peak-to-Average Ratio, Analyzing the reason, impair and distribution of high Peak-to-Average Ratio in OFDM system, researching methods of reducing PAR. Aiming at the defect that Compressing arithmetic plays down BER performance because of increasing noise when recover signal in OFDM receiver, proposing a kind of improvement scheme that adjustment expanding coefficient in receiver, the scheme can decrease BER effectively. Integrating Clipping and Compressing technique, proposing a combination scheme, studying indicates that the combination scheme can get better performance if system chooses suitable parameter on the basis of theoretic analyses and simulation. For solving inter-carriers interference that is caused by frequency offset and time-varying channel, study carrier synchronization technique of OFDM system. Discuss the influence of ICI caused by Doppler phenomena and frequency offset, provide the SNR loss caused by frequency offset. Summarize the existing carrier synchronization algorithm, Analyze merit and shortcoming of time-domain synchronization method, frequency-domain synchronization method and cyclic synchronization method by theoretic analyses and simulation. Propose a carrier synchronization scheme that append PN sequence in frequency-domain, through good self-correlation relevant characteristics of PN sequence estimate frequency offset, The arithmetic possess little calculating amount, good real-time character and better ability to resisting noise, can improve performance of frequency offset estimation and reduce ICI in OFDM system. On the basis of existing arithmetic, the dissertation puts forward improved algorithms and new settlement measure through studying reducing PAR and carrier synchronization technique in OFDM system. Research indicates that new schemes can reduce BER, improve performance of system effectively and realize high speed data transmission with OFDM.