Research Of Key Technologies On OFDM Data Transmission System In HF Communication

HF/UHF wireless communication transmitting requires only moderate transmitting power and reasonable equipment cost; while its channel is very difficult to be destroyed. These merits make its development very promising. Wireless communication systems are expected to provide high quality and high-rate mobile transmission. In order to achieve this objective, various technical challenges must be overcome. In recent years, Orthogonal Frequency Division Multiplexing (OFDM) has been applied widely in wireless communication systems due to its high data rate transmission capability with high bandwidth efficiency and its robustness to multi-path delay. However OFDM systems are vulnerable to synchronization errors. For example, carrier frequency offsets can lead to severe system degradation due to inter-cattier interference (ICI), while symbol timing synchronization must also be achieved in order to avoid inter-symbol interference (ISI).According to the influence of HF channel on data transmission, a burst MC data transmission scheme has been put forward based on orthogonal frequency division multiplexing (OFDM) technique. Then the system feasibility and key technologies have been described. It is efficient to use the multi-channel combination method to solve the rayleigh fading and group delay effect. Two key technologies, including synchronization and channel estimation, have been analyzed. In order to solve the synchronization problem under the condition of low SNR and large frequency offset, sliding correlation and frequency offset pre-compensation technique can be added. In addition, the system frequency offset is estimated by the iterative training symbol. Then the channel estimate method utilizing the training symbol and pilot is proposed.Finally, the system error rate is given. With the simulation of the Matlab software, the result shows that the system works well in low SNR condition.