Resarch On Applications Of Adaptive Beamforing Technology In OFDM Systems

Orthogonal Frequency Division Multiplexing(OFDM) is a kind of modulation technology, also a kind of multiplexing technology. The principle of OFDM is to split the serial transmitted data stream into N parallel streams of reduced data rata and to transmit each of them on orthogonal sub-carrier. The period of each code relative increase, this can reduce the inter-symbol interference caused by multi-path delay. In OFDM system each sub-carrier modulated signal spectrum has some part of overlapped, thus it makes the efficiency of frequency get great improvement. Nowadays,spectrum resource is becoming more and more scarce. Operators are very hard to increase the network capacity by expending spectrum again, in order to further improve the utilization of the spectrum, under the existing OFDM system, Operators use same frequency band in different cells or sections. This causes serious co-channel interference and decrease the performance of the system error rate, in the mean time it will lessen the coverage of the system, therefore restrain the co-channel interference is of great essential and practical. Adaptive beamforming technology is one of the key technology in smart antenna. The principle of this technology is making the antenna main lobe to the desired signals arrival directions and null steering to the interference arrival directions. So adaptive beamforming technology can overcome co-channel interference in OFDM systerm.This paper mainly researches the applications of adaptive beamforming technology in OFDM system, the job has been done are presented as follow:1. Researching the correlative synchronization of OFDM system. The paper analyzes the influence of symbol timing synchronization error, sampling error, carrier frequency error in OFDM system. S&C algorithm, Minn algorithm, Park algorithm, comparative analysis those algorithms advantages and disadvantages are simulated.2. Introducing the antenna array signal and direction of arrivals DOA estimation. By simulation, the performance of DOA estimation and DOA estimation based on music algorithm are compared and analyzed.3. Introducing various beamforming criteria and the main adaptive beamforming algorithms, classification and summary of various criteria and algorithms by graphs and tables.4. Studying the applications of adaptive beamforming based on DOA estimation in OFDM systems. The consequence of computer simulation indicates that adaptive beamforming can overcome the co-channel interference in OFDM systems. MIMO technology and smart antenna technology both are multi-antenna technology, they have common and significant difference. MIMO can exponential increase spectrum efficiency without adding frequency spectrum. This paper comparison MIMO and smart antenna from structure and principles, purpose a new system which combine MIMO, smart antennas and OFDM. This system greatly improved system performance and communication speed.