【作者】 孙山林；

【导师】 侯春萍；

【作者基本信息】 天津大学 ， 通信与信息系统， 2009， 博士

【摘要】 正交频分复用(Orthogonal Frequency Division Multiplexing , OFDM)是近年来备受关注的宽带无线传输技术。为进一步提高其效率和性能,本文将全相位FFT(All-Phase FFT, APFFT)技术引入到OFDM系统中,建立了全相位OFDM(All-Phase OFDM, APOFDM)系统。对于解决APOFDM系统的子载波间干扰(ICI)消除、同步、信道估计和峰均比(PAPR)降低等问题,以及有效的利用APOFDM系统特点实现系统性能改善,是本文解决的主要问题。根据APFFT的特点,本文设计了APOFDM系统的帧结构;分析了ICI对APOFDM系统的性能影响;并提出了符合全相位帧结构的同步算法;同时还进行了信道估计、PAPR降低和多维星座设计等方面的研究。第一,建立了APOFDM基带处理系统。APFFT能够较大的降低OFDM系统的ICI,并不会引入新的相位误差。在此基础上,得到了ICI引起APOFDM系统SNR下降的界,分析了ICI对系统SIR和BER的性能影响。研究结果表明:在APFFT处理下,OFDM系统的BER性能会得到很大的提高。第二,利用APOFDM系统的帧结构特点,建立了适于本系统的时域自相关频率估计算法。该算法不受载波相位偏移的影响,能够非常准确的得到频率偏移;同时也建立了最大自相关帧同步算法,该算法充分利用全相位数据在时域自我复制的特点,通过搜索相关峰值得到帧起始位置。该算法大大提高了系统对抗频率偏移的能力,在时变信道中能够稳健的实现同步保持。第三,根据系统在高密集热点地区对信道状态估计的要求,提出利用总最小二乘算法进行信道估计。该算法能够在快速时变信道中准确估计信道的变化,同时估计信道噪声对接收信号的影响,并利用最小范数得到最优解。仿真表明,本算法比较适合于多径衰落时变信道系统。第四,把DCT变换引入到OFDM系统,利用DCT具有线性变换和能量集中的特点,大大降低了OFDM系统的PAPR。该技术与传统的PAPR降低技术比具有运算量小、PAPR降低幅度大、不引入冗余及能保持系统BER恒定的优点。从理论上论证了多维星座设计在OFDM系统中能够大大降低终端的功耗,也提高了系统的误码性能,但其本身具有很大的运算复杂度。更多还原

【Abstract】 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.更多还原