隧道复杂多径环境下基于OFDM系统的信道估计

发布时间：2018-05-10 23:05

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

【摘要】：作为下一代移动通信LTE的核心技术,OFDM技术已经经历了多次跨越式的发展,越来越受到人们的青睐,其应用范围也在不断地扩大。隧道作为一种受限的通信环境,无线电波在隧道内的传播特性与非受限空间内的大不相同。受隧道壁的影响,传输环境中充满了电波的反射路径,在接收端产生多径效应,严重影响接收端对接收信号的解调,制约了无线通信系统在隧道中的应用。OFDM系统以其技术上的优势,能够有效地抵抗隧道环境下的多径效应,提高通信质量,使其成为隧道环境下进行无线通信的选择之一。作为OFDM技术的关键技术之一,信道估计在OFDM无线通信系统中占有非常重要的位置。通过OFDM信道估计技术,接收端可以获知无线信道的信息,结合接收端的均衡器,能够对接收信号所经历的信道衰落进行补偿,增强系统对无线信道衰落的抵抗力,提高通信系统的可靠性。本文围绕OFDM系统在隧道复杂多径环境下的信道估计展开,进行以下工作:1)分析无线电波在自由空间中的传播特性,包括无线电波的传输方式、无线电波的空间损耗及小尺度损耗。以此为基础,对隧道环境下无线电波的传播特性进行探究,分析无线电波在隧道环境下的传播损耗模型,然后建立隧道环境下无线信道的确定型模型和统计型模型,并对两种模型进行仿真分析。2)基于OFDM系统的基本原理、实现技术及关键技术,从OFDM系统的基带模型出发,研究OFDM系统基于辅助导频的信道估计算法和信道插值算法。根据直通隧道和弯曲隧道环境下的信道模型,利用Matlab仿真平台,对信道估计中的LS算法、MMSE算法、SVD算法以及基于小波降噪的信道估计算法在两种隧道环境下的估计性能作仿真和分析,并在直通隧道环境下对常数插值、线性插值、多项式插值、样条插值算法以及基于DFT的信道插值算法的插值性能进行分析和比较。3)研究基于DFT的信道算法,对尾部补零和降噪处理两种时域处理方式做了深入的研究和仿真分析。在此基础上,针对LS算法中易受噪声干扰的技术弊端,对基于DFT时域降噪的信道估计算法进行改进,根据信道响应中的噪声信号和有用信号设定阈值门限,对循环前缀内的信道响应作二次降噪处理。仿真结果表明,与传统时域降噪算法相比,改进后的算法能够获得3~6dB的性能提高。
[Abstract]:As the core technology of the next generation mobile communication LTE technology has experienced many leaps and bounds development and has been more and more favored by people and its application scope is also expanding. As a limited communication environment, the propagation characteristics of radio waves in tunnels are quite different from those in unconfined space. Under the influence of the tunnel wall, the transmission environment is filled with the reflection path of the radio wave, which produces the multipath effect at the receiving end, which seriously affects the demodulation of the received signal at the receiving end. It restricts the application of wireless communication system in tunnel. OFDM system can effectively resist the multipath effect in tunnel environment and improve the communication quality, making it one of the choices of wireless communication in tunnel environment. As one of the key technologies of OFDM, channel estimation plays an important role in OFDM wireless communication systems. Through the OFDM channel estimation technology, the receiver can get the information of the wireless channel, combined with the equalizer of the receiver, it can compensate the channel fading experienced by the received signal, and enhance the system's resistance to the wireless channel fading. Improve the reliability of communication system. In this paper, the channel estimation of OFDM system in complex multipath tunnel environment is carried out. The following work is done: 1) analyzing the propagation characteristics of radio waves in free space, including the transmission mode of radio waves. Space loss and small scale loss of radio waves. On this basis, the propagation characteristics of radio waves in tunnel environment are explored, and the propagation loss model of radio waves in tunnel environment is analyzed. Then, the deterministic and statistical models of wireless channel in tunnel environment are established. Based on the basic principle of OFDM system, the realization technology and the key technology, the channel estimation algorithm and channel interpolation algorithm based on auxiliary pilot in OFDM system are studied based on the baseband model of OFDM system. According to the channel model under the environment of through tunnel and curved tunnel, the Matlab simulation platform is used. This paper simulates and analyzes the estimation performance of LS algorithm MMSE algorithm and channel estimation algorithm based on wavelet denoising in two tunnel environments, and interpolates constants, linear interpolation, polynomial interpolation in through tunnel environment. The interpolation performance of spline interpolation algorithm and channel interpolation algorithm based on DFT are analyzed and compared. The channel algorithm based on DFT is studied and simulated. On this basis, the channel estimation algorithm based on DFT time domain noise reduction is improved, and the threshold is set according to the noise signal and useful signal in the channel response. The channel response within the cyclic prefix is reduced by quadratic noise reduction. The simulation results show that compared with the traditional time domain noise reduction algorithm, the improved algorithm can improve the performance of 3~6dB.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

【参考文献】