非合作通信中OFDM的定时载波同步方法研究

发布时间：2018-07-04 12:41

本文选题：非合作通信 + OFDM　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：非合作通信作为非授权接入的通信方式,是在不干扰合作通信双方正常通信的条件下接入到合作通信系统的通信方式。在非合作通信方式下,由于发端信息未知性以及信道干扰的复杂性,设计出符合性能要求的方法来实现OFDM系统的定时和载波同步是非常困难的,同时也是非合作通信环境下OFDM系统解调的关键技术。因此本文针对非合作通信下的OFDM同步技术进行了分析探讨,主要涉及到基于循环前缀(CP)的OFDM系统载波频率同步和基于偏置正交幅度调制(OQAM)的OFDM系统时频联合同步两个方面,所取得的主要解决方案如下所示:1.针对非合作通信下的通信系统的要求,由于低信噪比下载波频率同步性能不佳的情况,对基于循环前缀的OFDM系统载频同步进行了研究。通过分析接收端傅里叶变换后子载波信号幅度之间的关系,提出了一种多径信道下OFDM系统载频同步的方法,首先根据子载波信号之间的关系,初始构造出幅度差值代价函数;然后对其展开式推导消除无关项再次进行化简得到了基于幅度积的代价函数;最后通过分析幅度积代价函数的特性,将其等效为一正弦函数,进而通过多项式内插得到载波频率偏移估计值。仿真实验表明本文方法在低信噪比和多径信道下拥有良好的估计性能,且计算复杂度较低。2.在非合作通信环境下,对基于OQAM调制的OFDM系统进行系统符号定时和载频的联合同步研究。通过分析其信号的循环特性,提出了一种多径信道下符号定时和载波频率联合同步方法。该方法首先推导并研究OFDM/OQAM信号的周期平稳特性;其次通过对信号二阶循环特性的分析,表明了加性噪声对非零循环频率处的循环量不产生干扰;然后通过利用两对数值为偶数倍子载波间隔的循环频率,基于循环特性可独立得到符号定时偏移和载波频率偏移的估计表达式;最后通过对收端信号二阶循环累积量等的估计,从而得到符号定时偏移和载波频率偏移的估计值。仿真结果表明了定时偏移和载波频率偏移的估计不受到加性噪声的影响,以及两者之间估计的独立性,与理论分析相吻合,同时仿真结果也表明了在多径信道下该方法估计性能较好。
[Abstract]:Non-cooperative communication, as an unauthorized access mode, is a communication mode that can access cooperative communication system without interfering with the normal communication between the two sides of the cooperative communication. In non-cooperative communication mode, due to the unknown source information and the complexity of channel interference, it is very difficult to design a method to achieve timing and carrier synchronization in OFDM system. It is also the key technology of OFDM demodulation in non-cooperative communication environment. Therefore, this paper analyzes and discusses the OFDM synchronization technology in non-cooperative communication, mainly involves two aspects: carrier frequency synchronization based on cyclic prefix (CP) and joint time-frequency synchronization based on offset orthogonal amplitude modulation (OQAM). The main solution achieved is as follows: 1. To meet the requirements of non-cooperative communication systems, carrier frequency synchronization in OFDM systems based on cyclic prefix is studied because of the poor carrier frequency synchronization performance at low SNR. By analyzing the relationship between the amplitude of subcarrier signals after Fourier transform, a carrier frequency synchronization method for OFDM systems in multipath channels is proposed. Firstly, according to the relationship between sub-carrier signals, the cost function of amplitude difference is initially constructed. Then, the cost function based on amplitude product is obtained by simplifying the derivation and elimination of irrelevant terms, and the cost function is equivalent to a sinusoidal function by analyzing the characteristics of the cost function of amplitude product. Furthermore, the carrier frequency offset estimation is obtained by polynomial interpolation. Simulation results show that the proposed method has good estimation performance in low SNR and multipath channels, and its computational complexity is low. In non-cooperative communication environment, the joint synchronization of symbol timing and carrier frequency in OQAM modulated OFDM system is studied. By analyzing the cyclic characteristics of the signal, a joint symbol timing and carrier frequency synchronization method in multipath channel is proposed. The method first deduces and studies the periodic stationary characteristic of OFDM / OQAM signal, then through the analysis of the second order cycle characteristic of the signal, it shows that the additive noise does not interfere with the cycle quantity at the non-zero cycle frequency. Then, by using the cyclic frequency of double pairs of even times subcarrier spacing, the estimation expressions of symbol timing offset and carrier frequency offset can be independently obtained based on the cyclic characteristics. Finally, the second order cyclic cumulant of the receiver signal is estimated, and the second order cyclic cumulant of the receiver signal is estimated. Thus, the estimated values of symbol timing offset and carrier frequency offset are obtained. The simulation results show that the estimation of timing offset and carrier frequency offset is not affected by additive noise, and the estimation independence between them is consistent with the theoretical analysis. At the same time, the simulation results show that the performance of this method is good in multipath channel.
【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】：TN919.34

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