基于OFDM系统的定时同步与信道估计技术研究

发布时间：2018-06-06 03:41

本文选题：正交频分复用 + 多径信道　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：OFDM(Orthogonal Frequency Division Multiplexing)技术具有很高的频谱利用率以及较强的抗多径干扰能力,已经得到了广泛应用。然而,OFDM技术易受定时同步误差以及信道衰落等因素的影响。定时同步方面,本文针对最大似然估计定时同步算法需要事先知道信噪比信息,并且运算复杂度高的特点,介绍了一种改进方案,其定时性能与最大似然估计性能接近,并且易于硬件实现。针对SchmidlCox算法定时精度低以及硬件实现复杂,本文研究了利用滑动窗口对定时度量函数进行归一化操作的方法,该方法基本消除了峰值平顶问题,提高了符号定时精度,而且硬件实现更加简单。针对Minn方案以及Park方案存在较高的副峰,本文介绍了一种基于共轭对称序列的定时方案,该方案消除了副峰,产生类似理想冲击函数的尖峰,具有更好的定时误差估计性能。信道估计方面,本文研究了基于DFT(Discrete Fourier Transform)时域插值的信道估计算法,通过改进的阀值滤波法进一步消除了循环前缀内的噪声分量。该方法同样适用于存在脉冲噪声的通信系统。当多径信道的第一径不是最强径时,传统定时同步算法的定时位置将会位于瞬时能量相对最大的径上,而不是首径,这将导致FFT(Fast Fourier Transform)窗的起始位置落入数据域,产生严重的符号间干扰。通过对传统定时方案的细定时算法进行改进,本文重点研究了一种联合定时同步与信道估计算法。仿真表明,在普遍存在的复杂多径信道环境中,尤其当多径信道的首径不是最强径时,相比较传统的定时同步算法,联合算法仍然具有很高的定时精度,系统的信道估计性能也有了一定改善。
[Abstract]:OFDM(Orthogonal Frequency Division Multiplexing) technology has been widely used because of its high spectral efficiency and strong ability to resist multipath interference. However, OFDM technology is vulnerable to timing synchronization error and channel fading. In the aspect of timing synchronization, aiming at the fact that the maximum likelihood estimation (MLE) timing synchronization algorithm needs to know the signal-to-noise ratio (SNR) information in advance and the complexity of the algorithm is high, an improved scheme is introduced, the timing performance of which is close to that of the maximum likelihood estimation (MLE). And easy hardware implementation. In view of the low precision of SchmidlCox algorithm and the complexity of hardware implementation, this paper studies the method of normalizing the timing metric function by sliding window, which eliminates the peak flattening problem and improves the symbol timing precision. And the hardware implementation is simpler. In this paper, a timing scheme based on conjugate symmetric sequence is introduced for the Minn scheme and the Park scheme. The scheme eliminates the secondary peak and produces a spike similar to the ideal impulse function, which has better timing error estimation performance. In the aspect of channel estimation, the channel estimation algorithm based on DFT(Discrete Fourier transform interpolation in time domain is studied, and the noise component in cyclic prefix is further eliminated by the improved threshold filtering method. This method is also suitable for communication systems with impulse noise. When the first path of the multipath channel is not the strongest path, the timing position of the traditional timing synchronization algorithm will be located on the path with the highest instantaneous energy, rather than the first path, which will cause the starting position of the FFT(Fast Fourier transform window to fall into the data domain. Causing severe intersymbol interference. By improving the fine timing algorithm of the traditional timing scheme, this paper focuses on a joint timing synchronization and channel estimation algorithm. The simulation results show that in the complex multipath channel environment, especially when the first path of the multipath channel is not the strongest, compared with the traditional timing synchronization algorithm, the joint algorithm still has a high timing accuracy. The channel estimation performance of the system is also improved.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

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