【作者】 杨敏；

【导师】 王玲；

【作者基本信息】 湖南大学 ， 电子科学与技术， 2019， 硕士

【摘要】 随着通信技术的显著发展,人们多样化的信息需求也在急速增长,特别是对无线多媒体的需求尤为迫切,因此数据速率的要求也就越来越高,这使得宽带无线通信技术日益成熟并受到广泛使用。而OFDM(Orthogonal Frequency Division Multiplexing)技术作为一种多载波传输技术,因其实现简单、频带利用高、抗多径衰落能力和抗码间干扰能力强等诸多优点,已经成为无线通信系统最有前途的核心技术,并在数字电视广播、无线局域网和4G LTE等高速宽带数据传输系统中得到广泛应用。与此同时,由于通信设备的激增,电磁环境也愈加复杂多变,各种自然干扰和人为干扰都存在于通信环境之中。因此为了加强OFDM系统抵御各种干扰的能力,保障OFDM技术在干扰环境中传输的可靠性,本文从抗干扰同步技术以及干扰检测技术两个方面对OFDM系统中相关的干扰对抗技术进行了研究。首先针对OFDM系统中的传统同步算法所使用的训练序列在干扰环境下同步性能不理想的问题,本文对传统训练序列的结构进行改进并提出了一种新的同步算法,该算法利用了CAZAC(Constant Amplitude Zero Auto-Correlation)序列与加扰序列对传统训练序列的结构进行了重新设计,使其能够保持低频谱泄露的情况下完成在强干扰信号下的符号定时与载波同步。并且由于改进训练序列其结构及组成元素的特殊性,该同步算法可以以一种较低复杂度的硬件结构实现同步中的自相关运算,从而大大降低了乘法器的使用次数。接着本文对基于频域的干扰检测算法进行了研究,其中详细地阐述了连续均值去除(Consecutive Mean Excision,CME)算法与前向连续均值去除(Forward Consecutive Mean Excision,FCME)算法两种干扰检测算法的理论依据,并从计算机仿真的角度分别讨论了在不同干扰信号下窗函数、干扰噪声能量比以及帧数等因素对两种算法检测性能的影响。最后针对FCME算法时间复杂度较高的问题,本文对FCME算法的初始化过程进行了改进并提出了基于分块排序的FCME算法,该算法能够在较低时间复杂度的情况下保持与FCME算法相同的检测性能。更多还原

【Abstract】 With the development of communication technology,the demand for information,especially wireless multi-media and for high transmission speed is increasing day by day,which makes the wideband wireless communication technology become more and more mature and widely applicable in various fields.As a multi-carrier transmission technology,Orthogonal Frequency Division Multiplexing(OFDM),with the advantage of easy realization and high spectrum efficiency,can strongly combat multi-path and inter symbol interference,so it has become one of the most promising key technology in kinds of high-speed wideband wireless communication systems,including Digital Video Broadcasting(DVB),Wireless Local Area Network(WLAN)and 4G LTE.Meanwhile,the electromagnetic environment where exist various type of interference become increasingly complicated due to the rising number of communication equipment.In order to improve the anti-interference ability of OFDM system and guarantee the reliable data transmission,this paper will study the countermeasure technology of the OFDM system from two major aspects: anti-interference synchronization algorithm and interferen ce detection algorithm.To improve the performance of the synchronization in OFDM systems in the presence of interference,a new synchronization algorithm based on scrambl ing sequence is proposed in this paper,which redesigns the training sequence used in the algorithm with the constant amplitude zero auto-correlation(CAZAC)sequence and an extra scrambling operation.The new synchronization algorithm can still maintain the sharper correlation peak,and achieve accurate symbol timing estimation and carrier frequency offset estimation in the interference environment,with a lower out-of-band energy of the spectrum due to a new scrambling sequence.Furthermore,owing to the particularity of the component elements from scrambling sequence,a low complexity implementation structure is presented here to realize the correlation function of the proposed algorithm with less hardware resources.Finally,this paper does the research on the interference detection algorithm in the frequency domain,in which the principle of consecutive mean excision(CME)and forward consecutive mean excision(FCME)algorithms are analyzed in detail.Then through the simulation,this paper respectively discuss the influence of several factors(window functions,JNR and the length of the da ta)on the detection performance of these two algorithms.To reduce the time complexity of the FCME algorithm,we improve the data processing method in the initialization period and propose a new detection algorithm based on FCME,this new algorithm can ac hieve the same performance as FCME algorithm but with lower ti me complexity.更多还原