Study On Synchronization Technique In COFDM System And Its FPGA Realization

Recently, COFDM (Coded Orthogonal Frequency Division Multiplexing) technique has been paid more and more attention because of its strong transmission ability in wireless channels, which comes from its parallel transmission mechanism, inherited robustness to ISI (Inter Symbol Interference) and the diversity techniques of the multi-path channel. Meanwhile, COFDM system has very high channel utilization ratio because of the orthogonal properties among its sub carriers. However, COFDM is so sensitive to frequency offset, timing error and phase noise that a tiny synchronization offset may lead to the deterioration of the BER (Bit Error Rate) performance of system, even communication failure. As a result, in the COFDM system, how to synchronize in a quick and accurate manner is a very important issue, which affects the performance of the whole system. So the corresponding time and frequency synchronization algorithms should be proposed and realized in the COFDM receiver design.The OFDM technique has been adopted as their key technique, in more and more communication systems, with different application background, system parameters and data structures. This dissertation designs a entire synchronization scheme applied to COFDM systems, which is based on the surroundings of the aviation downstream data link system and the system parameters are designed in this dissertation.The development history and research actuality of OFDM technology has been reviewed in this dissertation. The basic principle of OFDM technology, technique feature and advantage are also expatiated in detail. A solution scheme for a high speed downlink wireless transceiver system is designed, based on intensive study of comprehensive performance and data transmission technology in the aviation data link system. In addition, a detailed theoretical analysis and simulation are employed to discuss the effect of synchronization offset on COFDM system. Some simple but practicable OFDM synchronization algorithms are presented based on the special system parameters and frame structure. Simulations are also used to make a detailed analysis of the estimation performance of algorithms.According to the performance requirements of the sync-system, a full synchronization system is designed on the basis of full consideration to the algorithms performance and realization complexity. In order to save logic resource, the method of time-division multiplexing is used to realize complex multiplication operation. CORDIC based complex phase extraction method is adopted to effectively guarantee the extraction accuracy of CFO (Carrier Frequency Offset).Finally, the performance of synchronization system is verified by the MODELSIM simulation tool. It has been synthesized and simulated in the chip of Altera. In addition, the entire COFDM transceiver system is debugged and tested through cooperation with other members of the project team. Test results indicate that the scheme of the sync-system can meet the practical requirements.