Research On Key Technology For All-Phase OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a major technology of broadband wireless transmission in recent years. In order to improve its efficiency and performance, all-phase FFT is introduced to OFDM systems and All-Phase OFDM system is established. However, there are many problems such as intercarrier interference (ICI) cancellation, synchronization of Carrier frequency, channel estimation and PAPR reducing that to be solved. How to using the characters of All-Phase OFDM system to realize the improvement of system performance is a challenge for receiver. Aiming at the problems mentioned above, the system frame structure is designed according to the feature of all phase FFT. ICI impacting on all-phase OFDM system is analyzed. Then the paper proposes the frame synchronization algorithm which conforms to the all phase frame structure. Finally, the channel estimation, PAPR reducing and the design of multidimensional constellation are studied.In this paper, all-phase OFDM system is established for the first time. ICI can be greatly reduced in all-phase OFDM system because of all phase FFT, and at the same time, the new phase error can not be introduced. The lower bound of SNR caused by ICI is obtained. We analyze SIR and BER performance with ICI. Finally, we get the conclusion that BER performance of system can be improved greatly with all- phase FFT.The correlation algorithm of frequency estimation in time domain is proposed in this paper. Making use of the frame structure of all-phase OFDM system, we obtain the accurate frequency offset and the estimator can not be affected by frequency phase offset. The maximum correlation frame timing algorithm is proposed, too. The copy of all phase OFDM data is used in this algorithm and the start of frame is attained with the peak of correlation. The algorithm greatly improves the system's ability resisting frequency offset and the healthy synchronization can be kept in time-varying channel.According to the requirement of channel state estimation in high-intensive user spots and high-speed mobile state which answer to the cooperation between base-band processing and antenna, the total least squares (TLS) channel estimation is proposed. This algorithm can accurately estimate the channel change in fast time-varying channel. And the channel noise can be estimated, too. The optimal solution of TLS can be received with minimum norm. The simulation results show that this algorithm is suitable for time-varying multi-path fading channel.DCT is introduced to reduce PAR of all-phase OFDM systems. With the application of the character of DCT energy concentration, the PAPR can be greatly reduced in all-phase OFDM system. Compared with the traditional algorithms of PAPR reduction, it has the advantages of small amount of computing and large reducting of amplitude. At the same time, it improves the BER performance of system.