Key Technologies In The Ofdm System

Orthogonal Frequency Division Multiplexing (OFDM) has better bandwidth efficiency and increased robustness to multipath fading and to interference than signal carrier adaptive equalization modulation techniques in wireless environment, OFDM has beco me the core technology of kind of data transmission due to its better characteristic. This paper concentrates on the key techniques in OFDM system. It also simulates by computer.Based on theoretical analysis and research of the mobile channel, firstly it introduces the basis principle of OFDM, including difference coding, the function of cycle prefix and so on. And it concisely presents an algorithm of reducing out-of-band emissions. Then we discuss the key techniques of OFDM concretely: synchronization and peak-to-average power ratio(PAPR), the results of simulations have been supplied. According to the results, the algorithm based on PN sequences can overcome the drawbacks of the algorithm based on cyclic prefix and get better synchronization in particular in the channel of strong interference and in the case of low SNR. The results of computer simulation have showed that the new algorithm based on orthogonal demodulation can ignore frequency offset and get better performance in the channel of low SNR. At the same time the transform of c rule, the transform of A rule, the transform of u rule and PTS, the soft clipping and the hard clipping can reduce PAPR of OFDM effectively. In the real systems we can combine these six algorithms and gain the best performance.